Fantasea sizing

I'm considering getting a fantasea fin with one of mertailors fabric tails in the near future and was wondering if anyone has insight on sizing. My feet are literally right between sizes. Most shoes I'm a 7.5 but sometimes am able to wear a 7. I'm nervous if I get the size that starts at 7.5 it would be too loose but at the same time my mahina is sized up, because my husband bought it and just hoped it was the right size, but that one has never slipped and the extra wiggle room just helps me get the fin on and off more quickly.
Anyways since they aren't adjustable I just wanted some feedback on whether the smaller or bigger size makes more sense.

Get bigger and wear neoprene socks to make it more snug

I'd go for a M!

I believe Mertailor uses the same foot molds for the Fantasea as for the monofin in the Spellbound. I have a Spellbound. I got the largest foot packet they have, which supposedly fits a size 12 mens foot. I am size 11.5, and it was so tight that I could only wear it for a short time, and even then it was painful. I made many measurements of my foot to see if it was oddly wide or thick, and found it is dead average for a 11.5 size foot. With some careful trimming of the silicone, I was able to make it tolerable.

Based on this: Mertailor's foot pockets are a little small. Go for the next size up. Use Trade Winds' suggestion if needed.

Ok thanks so much for your feedback! A medium it is.