For customization and fun, I made buttons from modelling clay. I used FIMO which needs to set in the oven, it comes in lovely colours.
Designs can be varied using glass beads, or layers of different colours, there’s also endless shapes one can make.
The flowers are made by flattening a cluster of 4 or 5 small balls.
I’ve washed the clothes with the ‘clay’ buttons often, no problem. Probably even tumble dried them. But avoid placing a hot iron on top, I mistakenly did it once, and it left a faint paler spot.