What type of lawyer do i need to write up an official lease and where can i find this type of lawyer?

I am renting to own a single wide trailer… I want to make sure once i start doing some minor repairs that they will not go back on the rather bland, rather short, lease agreement. I would hate to build up the house only to have them come back and say, "oh gee thanks for the house, but we would like to move back in now."
The mortgage is in their name and they rent it out to me due to the fact they do not know how to renovate or live in a single wide. They recently just bought a brick home that they moved into and say they just want the single wide off their hands.
What kind of lawyer do i need to speak with in order to write up a more solid lease, so that in the case they do change their mind or find a loop-hole, i will be re-imbursed for my repairs, materials, labor, etc. And where can i find a lawyer of this type?

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