I feel you fundamentally misunderstand how in ear buds work. Whether they fit your ears has nothing to do with their cost. You might get lucky with a £5 pair, or you might find a £500 does not happen to have tips that fit your particular anatomy. If are buying in ear the best thing to do is assume you’ll need to budget for some after market tips that fit you.
Absolutely true – I’ve never been able to get earphones to fit properly, with a pair of Etymotic headphones that I bought after people on here recommended them, I ended up spending another £120 on custom eartips in order to get decent isolation and bass!
I can’t wear them anymore because one of the cables has developed a fault. ☹️
With all the other earphones I’ve bought I found triple-flange eartips that would fit, and which give a decent seal, but no standard tips will fit my ears properly.
Apple EarPods do fit, but being shiny plastic there’s no grip, but I’ve just got some of the silicone covers mentioned above, and they really do seem to help them stay in place; I wouldn’t have bothered, but the nature of my job has changed slightly, and I’m in a position to be able to have earphones in, providing I can hear my radio in case someone needs help locating or starting a car, and EarPods are perfect, just because they don’t block outside sounds, tried them with the covers today, and they didn’t move at all. For about £7 for 6 pairs, I’m not complaining, I’ve got four sets of ‘Pods, so job jobbed.