Sole tenant wants additional occupier to help with rent

Tenancy Types and Management

I have a solo tenant that has been in one of my rentals for 5 years, has on 3 occasions had to approach me to put a payment plan in force when unexpected expenses have been incurred on their side which have been fulfilled with rent being brought up to date within 3 months each time. I am proposing to increase the rent due to my expenses increasing and the current rent is now well below market rate. They have advised that they will struggle to meet the uplifted rent amount on their own and have asked if I would consider an additional occupier to move in.

Current tenancy is standard AST rolling from initial 6 month expiry date.

I'm believe there are pros and cons of proceeding down this route and wondered if anyone else has added an occupier - what is best way of doing so, drawing up a new joint AST even though I expect the additional tenant will have no connection to the existing or drawing up 2 separate agreements for each tenant independently?

Many thanks