i'm having problems with condoms myself, i've always previously used normal condoms, not thinking why on earth i kept having them split and feel uncomfortable

ok, so not so bright i know but to be fair i blame sex ed in my highschool telling me all condoms are one size fits all lol.
so i've decided to move on to using larger condoms, but i want to buy them in shops, not order online. so far i've tried about 6 shops and none of them stock xl condoms! i'm getting pretty frustrated about the whole thing and personally i get mortified about the idea of asking over the counter if they stock them.
the only time i have asked was recently at a large boots shop, i just ended up stammering and turning bright red lol.