Remortgage or Loan

AliJW1

Am suffering with headfry so I hope someone would be kind enough to help me!
My partner is leaving me in my home which is worth about £290k with only a £20k mortgage outstanding (13 years remaining).
My only other debt is under £400 on an interest free credit card for my car.
I need to take back over the mortgage (which was in my name until 2017 when it was transfered to both names). I was on PAYE in 2007 when I purchased the house earning £285 net pw.
However am now self employed (have accounts back to 2012/3) and declare £8500 on average per annum.
I am 50yrs old, have had mortgages since I was 21 and never defaulted.
I need to pay my partner around £25k as he has done work on the house (am fortunate as he could have asked me for half forcing me to sell).
I am concerned that even though it is only £141 pm The Chelsea BS will charge me a huge fee to revalue/survey the house and take his name off and I may now even fail their financial eligibility tests despite the equity in my home.
Do I approach them and ask to remortgage to say £50k total (there is still work to do to the house which is essential)? Assume they wouldn't/not wise at my age extend the period of repayment to make it easier for me to afford.
Or would I be better off financially just getting them to switch £20k mortgage to my name and and seek a loan of £25k (if anyone would lend me this?). Assume if I went this route it would be better to do this once the Chelsea has done my eligability checks as a £25k loan (would have to be over a long time) would scare them off.
Try to switch to a new Mortgage lender afresh for £50k?
Finally I do have an option to cash in a pension in part when I am 55 to help pay off.
I will going forward try to increase my income now.
Please help - I cannot do the maths and am feeling pretty stressed about this all. Thanks so much