For starters: Do not use the cringles from a camping supply store!
Good equipment is expensive so ask your sail maker do do it for you. You have to go to him anyway to get the right sort of cringles. Also he will look at the sail and the corners to see if it is still strong enough or if it needs additional re-enforcement.
My sail maker charges me 2.50 to install a small cringle (the ones used for reefing ties), larger ones are more expensive obviously. For that money he also added a patch of cloth (sewn on) to re-enforce the area. A couple of years ago I had him check and repair an old main so I could use it as a spare cruising sail. The repair set me back 40 quid (today maybe that would be 80 quid). As an amateur I can’t compete with the quality and professionalism of a sail maker. Getting the right equipment would probably set me back a few thousand quid (or a few hundred if I can find it on eBay).
I say: leave it to the professional. Bring him your sail and ask for a quotation, quotations are given free of charge. Then decide what to do. I think you will be pleasantly surprised.
BTW, now is the time of year for a winter discount, don’t wait till spring when sail makers are overloaded with work.