How 'easy' is it to do a 'Deed of Variation' yourself during probate or should we get a solicitor?

Basically the title.
My ex's mother left us her house in a non-complicated will and I do not want it. We are doing probate ourselves due to it being a non complicated will.

We have spoken to a solicitor who has said it would cost £400 to draw up. However, from what I've read online it's a single sheet on paper simply laying out a few details LIke my name, the person who has died name and who i want my share to be passed to. Is that correct?

Some websites (Never believe what you read online though huh?) That you don't even need to do it if you're doing probate yourself as the probate people don't look at the will... I'm 99% sure that is B.S though.

Is it really as simple as the above? (Doing it yourself)
Anyhelp/advice would be very much welcome.

Additional info:
I was dating my ex when her mother (Lets call her my mother in law to make it easier but we aren't married) fell ill and we started to look after her. We moved into my Mother in laws house to help take care of her.
Sadly, me and my ex grew apart but we were still very good friends and I stayed living with her and my MiL to help take care of her. We said once her mother passed away we'd maybe live together for a bit but i'd move out etc. There is 0 Animosity etc

Sadly, my MiL passed away earlier this year and it turns out she left my ex and I the house in her will. I don't want the house obviously or ANYTHING else from the estate. The house is worth £140-150k(ish) and she had no savings, stocks etc.

We've decided to do probate ourselves as it's a non complicated estate/will and neither of us have any money at the moment due to paying for the funeral etc. We did have somebody who was going to help with probate (a solicitor friend) but his mother and father has just passed away suddenly and obviously I'm not going to ask him at this point now.