You could get adult sized OK stuff again years ago, I've still got a lovely 50s pump attendant's jacket... If you can be arsed it might be worth searching for them...
I'd recommend a trip to @JD's vintage emporium in Camden and grab a pair of OK or Lee dungarees... Late 70s soulboy classics...
Search for Osh Kosh (B'gosh), pricey but worth it...
Loads of kids stuff, their old workwear stuff is very much sought after by collector types...