You don't need boning caps, you can cut the boning with sturdy scissors and file them round to keep from getting sharp edges.
Synthetic whale bone. They used whale baleen as boning in corsets and stays thru out history. Of course we cannot use real whale bone any longer and it's completly animal unfriendly. However a boning manufacturer has now made a synthethic version of whale bone! Supple but sturdy and suitable to use in modern or historical corsets and stays. This is not like the cheap plasting boning you may find in bustiers, which can bend, break and generally hurt.
If you wish to go for fully boned corsets or stays , then I recommend 5mm wide boning. 7mm works for all corsets and stays.
Price per 5m or 25m.
5mm and 7mm wide and 1mm thick.
You don't need boning caps, you can cut the boning with sturdy scissors and file them round to keep from getting sharp edges. You can iron (on the lowest settting) this boning in case it retains it shape from being rolled up or if you need to shape it to suit your corset/bodice.