Hard to say without pictures of the now with regards to the look.
20" wheels aren't really an off-road wheel size, but you said you don't really go anyway. You will need to recalibrate your speedometer after you change tire size. The Jscan app mentioned all over the place on these forums can do that. Wranglers shift points are determined by the tire size setting that directly affects the speedometer. It won't drive right otherwise.
With a set of 33" tires, you will get a bit more power, and not pay as much for each tire. I don't know what sizes are available for that size wheel so you'll have to dig around. I would avoid tire sizes that are only available from one tire company. Go for a size that many of the companies make. They will be cheaper, and probably still around when it comes time to change tires again.
I would worry, (I would, not saying you will) that that size wheel and a smaller tire would start to look a bit wagon wheel or rubber band and a bike tire kinda thing. Some people like that look though.