Wirarpa pants, Amazon

[Bizarred]

I want to buy myself some of these in the high-waisted version, but am just looking for guidance on sizing, as they're not returnable.

I used to be a size 12 back in the 1980s, and although I am the same size now, I take a 10 most shops these days, apart from M&S when it can sometimes be an 8.

Any guidance? Should I get the pants in size S or M?

I am a size 10 top and 10/12 bottom and I bought a pack of Wirapa pants in M 3 months ago from Amazon - boyshorts with high waist- but wish I had opted for S as I find them a little big and I still get the dreaded "Wedgie" which was my reason for buying these as I constantly struggle with pants which ride up.☹️