question about vegetable-tanned soling leather

So, I hate to bother you, but I just cannot figure this out:  I wanted to get some veg-tanned leather (as you recommend) for topsoles, but when I went to look for it, there’s a dizzying variety.  There’s bellies, shoulders, double-shoulders, saddle skirting, tooling sides, culatta….

What in the world am I looking for?  I assume they have different properties, based on what part of the beast, but I don’t know what, or if they’re a moot point at this weight/for shoes.  I don’t want to get the wrong thing–leather’s too expensive for that!

answer: well, i don’t have the final word on that – i have purchased veg-tan from hide-house and wickett and craig – hide-house has it in every thickness, which is convenient, but I got the cheaper soling and it has a formaldehyde odor that doesn’t go away – wicket and craig only has thicker soling, it smells fine, which they will thin down but at increased cost. – although they do have “belt leather” that is maybe 4-5 ounce – I get “skirting” from wicket and craig, it’s a cheaper cut for one thing, and works fine… 8 – 10 oz. is what I get – best, sharon