A couple of things to help you, Collin.
The waders you're looking at are called "boot foot" waders becuse the boots are already attached. If you look around at fishing catalogs and websites, you'll also see "stocking foot" waders, which require a special pair of wading boots.
I don't think the Walmart waders are a good idea for one reason: They don't have felt or specialized rubber soles for fishing use.
If you plan to fish rivers, felt soles (or an all rubber sole called Aquastealth)are VERY important because they provide a good grip on slippery rocks. Normal "lug soles" like you see on hiking boots are dangerous on slippery rocks because they offer almost no grip. Obviously, when wading, the last thing you want to do is slip and fall.
Recently, some states have outlawed the use of felt soles because felt can trap and spread invasive plants and algea. You'll need to find out if this is the case in CO before you order. There are all rubber soles that offer better grip like felt, Auqastealth is one brand, there are others.
With boot foot waders, you order your normal shoe size.
Also, you MUST wear a wading belt. This is a belt that goes on around your waist on the outside of the waders. If you fall in, the belt slows the amount of water that comes into the waders.
Cabelas offers a reasonably priced
felt sole bootfoot. I'm sure you can find others locally.
Be very careful when wading in moving water. It's not really a good idea to fish alone until you have some experience. Never wade any deeper than your knees in fast water and always put one foot all the way down before moving the other foot.
Grouse