I strongly recommend that you join the NHF and make use of their legal services for drawing up a chair rental agreement that suits your needs.
https://www.nhbf.co.uk/membership/select-your-membership-package/
I’ve seen rental agreements on here in the past that geeks have ‘amended’ with their own clauses and when it comes to down to it, they’re not legally enforceable because they were incorrectly drafted.
Alternatively, find a local solicitor that deals with commercial law.
As a chair renter, you can offer your own contract and negotiate individual clauses with the landlord in order to find some suitable compromise.