Dr Chris McCarthy has a confession: "I am one of those people. I do take my pillow with me." You've seen his kind at the airport - pillow wedged under one arm while dragging a suitcase to check-in. Or perhaps you are his kind, loyal to a pillow soft enough to settle into but robust enough that it isn't bunched into a ball by morning.

McCarthy insists he isn't being fussy. He's a top physiotherapist, and he knows the wrong pillow can be a literal pain in the neck. He doesn't take his abroad, but the moment he reaches a hotel he starts "faffing about" with whatever pillows are provided, armed with a tried and tested trick to make even the most lacklustre cushion fit for sleep. Here's his guide - featured on the BBC's Sliced Bread podcast - to choosing the perfect pillow for you.

What makes the perfect pillow? One advertised for your sleeping position? Soft or firm? Feathers, foam or fibre? Sliced Bread separates science fact from marketing fiction. McCarthy, an associate professor at the Manchester School of Physiotherapy, says the right pillow depends on your sleeping position. Most people fall into one of three categories: side, back or front.

First, the bad news for stomach sleepers. McCarthy discourages front sleeping entirely, because your neck is turned one way for a long period of time. "Inevitably a muscle or ligament gets stretched and a bit irritated," he says. "If there's one thing there's a really good consensus on... in the physiotherapy world about treating spinal pain, it's don't sleep on your front."

For back sleepers, consider the flexion at the top of your spine - a curving that increases naturally in many people as they age. If you have a bigger bend, "it means you need a slightly thicker pillow than someone who's got a very flat back," says McCarthy.

For side sleepers, the key measurement is the width of your shoulders. Generally, the broader you are, the thicker the pillow you need. But your mattress matters too. McCarthy says how much you sink into your mattress "makes a huge difference in the subsequent height you then need from the pillow." In practice: "Broad shoulders need a thick pillow [if] you're on a very firm mattress. If you're on a softer mattress, then you need a thinner pillow because your shoulder sinks into the mattress [more]." This is less of an issue for back sleepers, who don't sink in as much as side sleepers do.

If your pillow feels too flat, McCarthy suggests placing a folded towel underneath and changing the number of folds to adjust the height. Then you can take a rough measurement to help you pick a new one.

Specialist pillows are often advertised as contoured, ergonomic or orthopaedic - but McCarthy says their effectiveness isn't completely proven. "There is a little bit of fairly scrappy evidence to suggest that having a little bit of a higher front of the pillow, which goes into the neck area... does help [side sleepers]." To test whether a higher front helps you, try McCarthy's towel trick by rolling it and placing it underneath your pillow. He urges side sleepers to pick a position that keeps their back straight.

For back sleepers, some manufacturers advertise a pillow with a dip in the middle that is raised at the sides. It does put people into a good sleeping position, says McCarthy, but some of his patients have found them "a bit claustrophobic." Someone with a large and heavy head also needs a thicker and firmer pillow, he adds.

Material matters too. Feather and down can keep you cool on warm nights because they wick away heat from your head, says McCarthy. But they can change shape during the night, particularly if the sleeper moves around a lot, and the pillow can end up bunched towards the headboard. "What starts off as a nice, flat, supported surface becomes a wedge and so your neck is then kinked up." Hollow fibre and microfibre fillings can hold shape better, though they generally don't wick away heat as well. Some are made with a firmer material in the lower half, which helps retain shape during the night.

McCarthy bought his own foam pillow - which has tubular spaces for ventilation - five years ago for about £50. As a side sleeper, he adjusts its height using a folded towel laid underneath. He says choosing the right pillow is very much "horses for courses" and encourages people to use the trial period some manufacturers offer. "There just isn't a one-off design that is perfect for everybody or every position, I'm afraid," he says. "You really have to personalise it."