Here's my attempt at a "beginners" ball - stretcher
it's a leather luggage label strap with attachments made of wash leather where the loops are formed using super glue.
Plenty of talcum powder is needed to avoid pinching the skin. You may have to make an additional hole to ensure a snug fit.
Any old weight can then be attached. Here I'm using a large socket weighing about 300 Gms.