Stock driver's seat has a little play
 

When I get into the car and jerk back a little, the seat moves. And not like a little flex, more like somethings loose and there's some play. Has anyone had this problem or know how to go about fixing it? It's mid-winter so it's hard to do car maintenance at the moment so just researching before I take a look.

Check your bolts. You could try re-poditioning them and re-tightening in a different order. Most, if not call cars I've been in have a little seat wiggle. If it's clunking, something is either bent, bolted down wrong, or whatever it is bolted to is giving way

I tried sitting in the passenger seat and had the same type of play, so it might just be the way it comes, considering that passenger one has had someone in it maybe 5 times in it's entire life haha

Yeah the one in my car rocks a little bit if I'm trying to make it by being bouncy! I wouldn't worry, great observation though!