I originally used a racing undersuit made by EDZ. Was great, but if the velcro ever got hold of it, it started to pull it apart, plus it started to lose a bit of it's darkness over the years I had it. Ended up a very dark grey, rather than black.
A few other guys used racing suits made by Receka, but their customer service let them down very badly.
I ended up biting the bullet, and spent out on a set of Underarmor. Best money I ever spent TBH. Fits a treat & very comfortable. Helps absorb the pain of 'trooper pinch' too.