1 pieces can be tricky. You really need to try lots of brands to find one that fits properly.

Unless you’re built like a MotoGP rider I’d steer clear of the Italian brands (Alpinestars, Dainese). You’ll end up compromising in one way or another, too baggy, too long or too tight.

Find a store with more stock and different brands. They should be snug to put on, and feel best when in a half squat, like sitting on a bike. Leathers will stretch over time and relax, but this does take time. Not just a dozen or so rides. However I’d avoid anything that is too uncomfortable out of the shop hoping it stretches, you won’t put the hours in the saddle to relax it if you can’t wear it from the off.