I wear contacts & recently needed to add bifocals/readers. Tried the "silicone glue-on" magnifiers the lds recommended & after drying they came off immediately in my home test bucket the next day. Re-glued them on (& left them alone, this time). Packed for a trip & they came loose during my second mask rinse, day 1. Aaargh. Went without "magnification", the rest of the trip.
Back home, talked to my optometrist, & got "mono-vision" in one my contacts. Works great! One eye sees long distance best, the other eye can see long distance, but also sees close-up, for gauge reading or critters.
So, OP, if the prescription lenses & after-market "add-ons" aren't working, consider disposable (biweekly/monthly) contacts - 1 of them with monovision - at least for diving. I much prefer contacts, especially UW, over glasses/inserts (but haven't tried or paid the big bucks for a prescription/bifocal mask). Plus, I have a small face & had a difficult time finding a good mask that fit originally. I do shut my eyes when clearing my mask, but otherwise contacts have never been an issue. (And I always pack a reserve pair - just in case). Just another option . . .