Mastercraft seats are really nice but more on the $pricey" side, I have Beard Ultras and they are very comfortable, the Beard super seats are a bit cheaper but not quite as cushy, PRP makes some nice seats, I have a set of Hunsaker Envy seats here, they are ok but much cheaper than the others listed, they are made a few miles from my shop, all those listed accept full harnesses. I'm not sure if you have a cage but it is generally a bad idea to use harnesses w/out one, I'm sure you know this but thought it would be worth mentioning for others that may be reading this thread. Good luck, I know the guys over at hunsaker if you wanted me to set you up, I could probably get you a better deal if you wanted to go that route. The beard and prp seats have tabs for mounting, regular width are 14" x 18" with the wider version being 16" x 18" just fyi.
good luck
Chris