I was in the same boat last summer when I started playing again after 20 years. I didn't even know it was common to use that grip for a serve. I had a really flat serve with a small margin for error just like you. I ended up successfully switching up my grip and developing a better first and second kick serve but it took quite a few baskets of balls and a lot of repetition. The end result was a better first serve with less pace and a stronger second serve. My previous "Cinder-fella" second serve was getting walloped.
I only double fault 2 or 3 times in a three set match now.
NTRP 3.5 with < 130mph TTW serve | Head Microgel Radical MP (3g split at 3&9, 5g in handle) | Babolat Xcel French Open 16ga @ 58 | Year 2 of playing