What cardstock do I use?

Hi everyone! I have a question about a project I have in mind but am not quite sure about how to execute. I want to print out multiple copies of a photo and send it to family members with a photo mat that I will foil using my minc (basically have it ready for them to frame). Should I make my own photo mat with cardstock and then foil it? Or can I buy readymade photo mats (where from?) and then print and foil on them?

If you think I should use cardstock and create a mat myself, any recommendations on what kind to use?

Thank you!