"Hey, Love your site, I'm new to bikes and it's helped me loads when picking the right gear! I just bought a set of leathers from ebay (risky for sizing but I have textiles in the same brand and they fit) the thing is the leather is really quite tight. I can get them on and zipped up but walking seems like an effort! Are they supposed to be so fitted? Or will they loosen off with use? Or should I have gone up a size?!" - Kristen
They should definitely fit very snug. If you're having trouble walking upright, that's probably the right fit :)
Ideally, your one piece suit is fitted and designed for riding position only. It assumes that you'll be spending most of the time on the bike. If you're riding a sportbike, then it definitely will be more comfortable on the bike than off.
You can tell if it's too tight if you can't inhale/exhale comfortably, or if there's pinching or pulling under the armpits and around the crook of your elbow and behind your knees.
A photo of you on your bike would help greatly, but it sounds like you've found the right fit if it's a brand new suit and hasn't been broken in yet. If you're buying a set of used leathers that someone has definitely broken in, then in that case, I could see the suit not being the right size or fit.
Unfortunately, leathers are quite uncomfortable until they're fully broken in, but hopefully after you've spent some time making them feel like second skin, you'll love spending every minute in them.