I had a onesie from 'back home' in 1970- it was bright orange, with feet on, like a giant babygrow. Had it for years and years- I wore it for a fancy dress party in 79, I think, with a pair of big baggy frilly pants (versize tennis pants) over- and a dummy. LOL very fetching (I was skinny then)- and it must have gone in the bin after that.
We bought DD1 a tartan onesie when she was sharing a Victorian conversion near Aston Uni with other students, she had one of the attic rooms and it was freezing - she loved it. We hired a cottage in the Cotswolds just after her graduation, and she used to sit with the dog (her all time favourite) on the patio, in his basket, onesie on. And the old lady who owned the place said to her 'Have you taken yor O'levels yet Claire?'- she was 22.
DD2 bought herself and both her niece and nephew a onesie for Xmas- and they lived in them ever since. DD1 and family have just gone home, but DD2 is on the settee in hers...
Best if I don't indulge in one though;) (size 18 + Xmas indulgence).