Forget you ever heard the term 'offset' which while useful for car wheels, isn't as useful for fitting Jeep and truck wheels. The two terms are different measurements and are not interchangeable. Focus on the wheel's backpace dimension, that is all you need to worry about.
If you offroad, you want to stay with a 15x8 wheel for 33x12.50 or 35x12.50 tires. A 15x10 is fine for paved road use but for offroading where you air your tires down, those two sizes of tires will be able to stay safely seated when aired down for offroading far more easily on a 15x8 wheel than on a 15x10.
Put differently, it takes more air pressure to hold a tire safely seated against two edges that are 10" apart than if they are only 8" apart... a key thing when you want to air your tires down for offroading.
Backspacing wise, anywhere between 3.75" and 4.5" works fine. You'll need to add a washer or two under each of the two steering stop bolts if the wheel has 4.5" of backspacing but that's no big deal... takes 5 minutes and ten cents worth of washers to do that. The benefit to that much (4.5") backspacing is the tires and wheels don't stick out as much as they do with less backspacing like 3.75". I prefer 4.5" myself.
This is how backspacing is measured... backspacing is the distance between the wheel's mounting flange surface and the inner most edge of the wheel. The yellow tape measure is measuring the backpacing. The more backspacing a wheel has, the more "inward" it is positioned. A wheel with very little backspacing will make a vehicle look like a skateboard..