I like your idea,but it has possible problems.
Just as native Cubans are still restricted (in many ways) from meeting/mixing socially with tourists,the reverse works.
You may find that tourists are only allowed to stay in designated "tourist" hotels,and not the character or local ones that you want.
Of course now that the country is being run by Fidel Castro's brother,things may have relaxed somewhat,but I doubt it.
If someone has a hotel they can recommend then try and book and see,but don't be surprised if you can't/
Of course it depends what you mean by "not commercialised"?