In terms of disabled access the building regs now require that all ground floor rooms in new builds or major reconfigurations are wheelchair accessible, including front doors and interior doors and also that light switches and electric sockets are halfway down the wall for the same reason.
I think there has to be a downstairs loo too, in addition to any that are fitted upstairs if relevant,mand there has to be clear wheelchair roll room to everything. However the bath etc dont have to be disabled accessible as that can be add on retro fitted whereas the rest has to be done at the outset.
Hence our PP for restoring and renovating a ruined cottage on our farm has all that plus you have to have access without steps from car parking to front door so theres a long ramp.
NB shower trays are generally low lip these days, there isn't a requirement for a wet room roll in shower so unless that's been chosen that might have to be retrofitted if you wanted to go for full wheelchair access.
So, in theory, if you initially concentrated on recently built or recently completely renovated single storey properties or one with maybe just occasional guest rooms upstairs eg in a dormer to minimise the need to use the stairs, you ought to find pretty good Holiday let /disabled access built in, with just extra kit to add if you want to have accessible baths with hoists, handrails on ramp up to front door etc.
Hope this helps a bit, we had no issues with the regs as the cottage is intended either for elderly parents or as holiday let, either of which make the requirements a benefit.