Most people buy a home office chair the way they buy a kettle: pick one that looks sensible, read a few reviews, order it. Then they sit in it for six hours a day and discover the seat is two centimetres too deep. A chair is the one piece of home office kit you cannot work around. A wobbly desk can be shimmed, a slow laptop can be tolerated, but a chair that fights your posture will grind you down by Thursday afternoon. The mistakes below come up again and again, and most of them are made before the chair even arrives.

Buying the chair before you've measured the desk

Chairs and desks have to agree with each other. Most desks sit somewhere around 72cm to 75cm high, and a kitchen table is usually taller than people expect. If the chair's lowest seat height leaves your feet dangling, or its highest leaves your knees crammed against the underside of a drawer, no amount of lumbar padding will rescue the setup.

What you're aiming for: feet flat on the floor, thighs level or sloping very slightly down, elbows bent to roughly 90 degrees and shoulders relaxed rather than creeping up towards your ears. That last point is why the seat height range matters more than the maximum figure. A chair that adjusts down to 42cm suits a very different person from one that stops at 48cm.

Then check the desk itself. Armrests taller than the gap beneath your desk will stop the chair rolling close enough, and you'll spend the day leaning forward to reach the keyboard. Measure that clearance before you order anything.

Getting seat depth wrong

Seat depth is the measurement people forget and notice last. It's the distance from the front edge of the seat to the backrest, and it decides whether the chair supports your thighs or cuts into them.

Too deep and you perch on the front edge to keep the back of your knees clear, which means the backrest is doing nothing at all. Too shallow and your thighs take weight they shouldn't, and you slide forward without realising. The usual guide is a gap of roughly two to three fingers between the back of your knee and the front edge of the seat.

Plenty of chairs don't let you adjust this, so measure yourself first. Sit upright against a wall with your feet flat and measure from the wall to the back of your knee. That number is your seat depth, give or take a centimetre.

A two-minute check

Sit with your back against the backrest, both feet flat. Slide three fingers into the gap behind your knee. If they fit comfortably, the depth is about right. If they're squashed, the seat is too deep; if there's room for your whole hand, it's too shallow. Remember that a chunky lumbar cushion pushes you forward and effectively shortens the seat, so judge depth with the support in place.

Treating armrests as an afterthought

Armrests are the difference between a chair you can sit in for a long day and one you quietly resent. Fixed-height armrests are the usual problem. Set too high, they push your shoulders up; too low, you slump sideways to rest an elbow.

Height adjustment is the feature worth paying for. Set the armrests so your shoulders stay down and your forearms rest at roughly desk height, not above it. If you use a keyboard tray, play guitar, or simply want to pull the chair right up to the desk, look for flip-up or removable armrests instead.

Material matters too. Hard plastic edges press into your forearms after an hour. If you already get elbow or wrist discomfort, padded armrests wide enough to rest on rather than perch on make a genuine difference.

Assuming "lumbar support" means the support suits you

Nearly every chair listing mentions lumbar support. On a surprising number of chairs, it means a fixed foam bump in a fixed position, shaped around an average body that probably isn't yours.

What matters is where the support sits and whether you can move it. Your lumbar curve is in the small of your back, around waist height, not halfway up your spine. On a chair built for someone around 185cm tall, that bump lands near your shoulder blades if you're closer to 160cm. Up-and-down adjustment is the minimum; depth or firmness adjustment is better still.

Two more things to check while you're there. Can the backrest recline a little and lock, so you can change position through the day instead of sitting rigid? And does the seat have a waterfall front edge, so it doesn't dig into the back of your thighs? A chair that offers one fixed posture is a chair you'll start avoiding by mid-afternoon.

Skimming the returns and warranty small print

A chair is one of the few things you genuinely cannot judge until it's in your room, at your desk, with your monitor in front of you. That makes the return policy part of the product.

When you buy online in the UK, you'll generally have 14 days from delivery to cancel the order under consumer protection rules. What varies is everything around that:

• Who pays return carriage, and whether you have to arrange the courier yourself.
• Whether the chair must go back in its original packaging, dismantled.
• Whether the window changes for sale or clearance items.
• How long the warranty runs, and whether it covers the gas lift, castors and mesh — the parts that actually fail.

Chairs are bulky and heavy. A return that sounds free can turn into a pallet, a courier quote and a trip to the post office. Read the terms before ordering, keep the box for a fortnight, and if you're buying secondhand, sit in the chair before money changes hands. This is general information rather than legal advice, so check the seller's own terms and take proper advice if a dispute gets serious.

A chair you stop noticing

The best home office chair is the one you forget about. You won't get there from a specification sheet alone, but you can get close by measuring your seat depth and desk clearance first, buying from a seller whose return policy you've actually read, and spending the first week adjusting rather than accepting the factory setup.

When the chair arrives, work through it in this order:

1. Set the seat height so your feet are flat and your thighs are level.
2. Set the armrest

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