Give notice
Option 1
Convert attic to ensuite, furnish as bedroom.
Depending on your layout, add or remove an internal wall.
for example one or more of the following:
Use the box room to make a bedroom into an ensuite.
Redo the kitchen into kitchen / common room
Take out the fireplace & make the living room a bedroom
Get your BER up (depends on what your BER is now)
Make sure you have fully documented, photos, engineers report, contractor invoices.
option 2 - leave property untenanted for 2 years
And then re-let at market rate, and ditch the agent. In my opinion, no one looks after your business as well as you do.