There is currently one property in Farmington, in the southern metro area, which is a historic site which already has a conditional use permit for a bed & breakfast. It is listed at $449,000 and has 4 bedrooms and 4 baths and several common areas. That property would be ready to go and would conform to your use right away.
There are also a number of larger single family homes which are currently zoned commercial, which would make your proposed use doable pretty much right away. Otherwise, as others have mentioned, it would be necessary to investigate the likelihood of pursuing a zoning change in your chosen area, which is by no means impossible, but should be undertaken with a strong commitment to due diligence prior to purchase.
I hope that helps.