So yesterday my favourite bra began to move about. Band felt looser and the cups were riding up on me. I assumed the elastic had gone and would need to buy a replacement but thought I better measure myself just in case.
Favourite bra is a full cup tshirt with underwire and moulded cup size 34E.
Your measurements suggest a 36Ff as a starting point - however it's not uncommon to wear a smaller band than you measure. How old is the current one- they can stretch a lot so you might find your old 34 is bigger than a new 36. Fantasie run biggish in the band too.
Pop your current bra on and scoop all the tissue under your arms and round the back forward in to the cups. I suspect you'll find you have quad boob