I don't think it would be complicated from a building POV, but I think you would need to wade through a whole load of bureaucracy and H&S requirements, e.g.... - Apply for a change of use, to turn a resi property into a B&B/business - Comply with all sorts of H&S requirements that are much stricter for businesses than homes - e.g. fire doors and escapes, extinguishers, alarms, tests/inspections, etc. - I guess there'd by implications for your kitchen too - H&S and food hygene...?
You might also be liable for business rates as well as council tax on the rest of your house.
I used to work in council tax and business rates and there was a woman who converted her garage to use as a therapy/massage centre and her business rates amount was awful and she had to shut her business down.
Plus all the insurance and my mate makes cakes as a sideline but had to rip out her wooden floor of her kitchen as it wasn't considered to be hygienic enough to get her food safety certificate (it was almost brand new wood flooring too)
It may not be financially viable for just one room but you could certainly investigate. Sometimes other B&B owners are happy to share the ups and downs.