Ok we will get married then. I know we still need some proof cohabitation when married too but that shouldn't be as much of a headache. Would we have to show as proof the bills, accounts etc after the marriage period or before too? We will apply quite soon after.
Before will help establish that you have been living together before (relationship bona fides), you should at least have something 'current' for after the marriage.
Note, since married, you can write a letter of explanation that you were living together from [whatever actual date is], but that you only have a few basic bills as retained mailing address elsewhere for a while [for whatever reason].
Evidence that is very weak for common law purposes can be perfectly fine for showing living together before married - it's just more relationship evidence.