Adding my $.03;
A good solid purpose-made belt is a necessity for belt carry of a sidearm.
1 1/2" width is ideal IME.
A lot of folks find 1 1/4" to be enough, but if you're carrying a heavy gun, say 36 oz or more, 1 1/2" will be more comfortable.
1 3/4" is fine, but only jeans and work pants will accomodate that width, and that won't work for me.
Some folks find that a 1 1/2" belt tapered to 1 1/4" in front enhances concealment (the visible part in front looks more like a dress belt), though I just usually just go with 1 1/2" width all the way around.
FWIW, there are none better than Lou Alessi's IF you need a belt that LOOKS like a dress belt AND lasts forever AND works well. Lou skives the belt so it's thinner at the edges than at the center, which other makers will do as an "extra" feature, though Lou's belts have this feature routinely.
If you just want support but don't care as much about details of appearance or about durability, you have LOTS of alternative choices, and even durability plus support can be had for very reasonable prices, eg. Uncle Mike's polymer belts and the Wilderness 5-stitch belt.
Personally, I haven't found it to matter whether a belt is cut on a contour or not. If you wear a belt, it will develop a contour. Period. Doesn't matter if it was straight to begin with.
If you buy it already contoured, I suppose some might find it more comfortable from the outset, though it's never mattered to me, and I wouldn't pay more to get this feature, but that's JMNSHO.
I've had belts from almost every maker out there, and Alessi's are my favorite, which is not to say that others aren't just as good, just that they don't quite look as "dressy", which happens to be important in my particular situation.
YMMV, etc.