Glock makes basically 3 models for each calibre. The Glock 21 is .45ACP. In 9mm there is the full size Model 17 with 5 inch bbl, than #19 with 4.25" and the Model 26 that has 3.5 inch bbl. The Glock 20 and 21 are larger than the other Glocks due to being 10mm and .45ACP calibre. The thee 10mm guns are Model 20, 29 & G30, there is also G20SF, G29SF and G30SF. In .45ACP there is the G21, full size than G31 and G36 and there the SF which are smaller grips. The shorter bbl Glocks we cannot get and the shorter guns are really hard to shoot if we could get them.I want to thank everyone who posted so far who's helped me with valuable information. Just been looking into Glocks so far and the Glock G21 (Gen4) stands out, comes in 9 mm and .45 ACP and is within my price range. I think that's the closest so far I've come to finding something I'd really like. Are their any other polymer framed semi-autos that are a little more ergonomic than a Glock?
I think what your referring to is the Glock 17 and the Glock 22 are basically the same gun but one is 9mm the other is .40S&W. If you were to buy the G22 you could put G17 parts in it or convert it to 9mm fairly easily.
The Glock 17 was the origional Glock and is still the best followed closely by the G19 which is a little smaller all round. You cannot fire lead bullets in the Glock due to it's bbl design and the Glock kicks more than a steel gun due to it's light weight. It might be worth your while to buy a good book about the Glocks and read up on them.