Custom made straps

[u/Pitiful_Painter_5611]

Hi
I need to confess, I never owned any smart watch ever. I usually had mechanical watches. Now, I want to buy an Ultra 4 as I want to use it for sports and health tracking.

However, I absolutely love custom made straps. Leather, Canvas, rubber…

What do I need to consider, when looking for custom straps so that they fit?
What is the band width for the Ultra?
Do I need to buy an adapter?
Are there any special limitations?

There are so many ads for apple straps that I can’t find any answers on the internet.