Nostril stud -what size to buy & where? - UK

what's the best size stud for a nostril piercing? I went to a shop today who said 0.8mm and the 1.2mm is too wide.

I want a flat back labret, as my current one (the hook/c shape) is snagging inside and is now actually too long so also sticking out my nose.

The piercing is 4 months old and desperately needs a change with it sticking out and getting irritated again but the piercing shops near me only stock the basic balls or the diamond style which I don't want so I need to order online.

any suggestions? I've gone through so many shops on the lists and have no idea what I need.

is 4 months too early for a hoop yet?

UK based shops and suggestions only please.