This is what I find confusing. You talk about code and mm gauge. With O scale I know what goes or works with Lionel and have a nice layout. I use a 36 curve which works well. They have wider curves such as a 54 and 72 which is a wider area for turns. If I want to find out more about code and gauge where would I find this information?
The code relates to the cross section and principally the height of the rail.
So, of all the readily available 45 mm gauge track, code 332 rail is the most common - LGB, Piko, Accucraft, (Aristocraft and USAT when they were in production but still available second hand) and in Europe, Train Line. All of these are brass rail, and all of these are compatible.
Peco, and some US suppliers make 45 mm gauge track in a code 250 rail, so the rail height above the sleepers is lower. However, most rolling stock will run on this track, although LGB locos with skates have am electrical problem going through Peco points (turnouts).
As to the curves, here you get into further issues:
LGB make track with a diameter as small as 4 ft, which is very tight, and they adapt their loco and rolling stock chassis to suit this very tight curvature. Pik, I believe are similar.
Most US manufacturers recommend 8 ft diameter as a minimum radius for their models, and all of the code 332 manufacturers make track od this radius and larger.
See if I can find some links

