I have seen the snaps and like the idea, but does it hold as snug as a holster with belt slots in it?
From a quality maker, yes. The snaps will be "one-way" snaps that only release when pried up in a certain direction, so they can't come loose accidentally.
Also with a pancake, should I find a holster with a backing to it that keeps the butt from touching my skin? I would think it would be more comfortable but maybe cause it to stick out further?
A 'sweat-shield' is what you're referring to. I've never seen a holster that had one that covered the entire butt of the gun, as the butt doesn't really ride against you, usually. Most sweat shields cover the back of the slide and whatever safety levers, decocking levers, and slide serrations there might be, and keep the corner of the back of the slide from digging into you. On an IWB, that's pretty important. On an OWB, not so much, but that all depends on your body shape. If you tend to 'lap over' a bit on the sides, it may make it more comfortable.
Any more suggestions on a good pancake?
I use a DeSantis "Speed Scabbard" but most of the makers put out one version of this or another.
You should decide if you want a thumb-break retention strap or not. Some makers have them, some don't, some give you the choice. (I don't use them, myself.)
Also where can I find a good affordable belt? What width should I look for with jeans?
Beltman leather is a very good maker for a leather belt.
Wilderness Tactical makes some very good synthetic belts, either the '5-stitch' or 'Instructor' model offer a lot of support.
For jeans, I really like a 1-3/4" belt as that gives the very best support and digs in the least. Most guys buy 1-1/2" though. Don't go smaller than that unless you have to to fit dress slacks.