I have some wet okole seat covers . I love them. They look factory and are really comfy. They are also a bit pricey. I think 500 to 650 a set front and rear.
The only thing is they fade after a bit . I have had these 4 yrs and the sun is fading them.
I've had the Wet Okole ones in a previous TJ, did not get them for my last JK, and now plan to get them this spring for my current JK.
If you leave the top off most of the summer like I do, they really make a difference in stopping the seats from fading. Yes, the seat covers fade over time but I'd rather them fade than the actual seats. As StereoGuy said, they are sort of pricey, but I think they are worth it.
Once you get them put on and tightened up, you shouldn't notice them coming loose - at least I never did.
I had my previous JK from 2008 until last spring and had the doors and top off from about now until the start of October every year and the seats were faded pretty badly from so much exposure to the sun. It was definitely noticeable.
I would echo WSU JK's response - even the cheaper Smitty Bilt neoprene covers I purchased years ago stayed snug until they started to fade from the sun, about 3 years or so. But in that time they soaked up a lot of abuse that the stock seat covers would have absorbed. Mine were the covers with all of the pockets on the back, they started to show some wear around the seams and stress points about the time they started fading but overall I was happy with them.
I put a set of wet okole's on my tj in 04 when I bought it new. Just went and looked at then. Still look great. Thats with two kids growing up from birth till now. (7 and 9)
and even the seat backs still look great.