@Louise532:
Sorry about a bit more rain... Your landlord's insurance policy will most likely NOT cover short term rentals. Short term rental policies are more expensive and there are only a couple companies who offer them. I would be surprised if he would be willing to pay the higher rates for something that he will not financially benefit from, but will directly negatively impact his finances from additional wear and tear.
You cannot get a policy on the property because you don't own it. Your renter's insurance will not cover sublet damage either as it only covers you and/or your family.
One more thing- check your lease. It probably prevents subletting too. If, by chance, your landlord does approve the room rental, then be sure to add an adendum to your lease.