got a focefield pro sub 4 back porotector myself. best back protector on the market if you look at the stats.
it is a thick back protector, and gradually moulds to your shape with the heat. never found any discomfort with it whilst on the vee. keeps the back nice and warm on the cold days though. there is slimmer versions and different models but don't offer the excellent protection the pro sub 4 does. think the next one down is the "L2"