Advice on partner moving in and paying off mortgage

My partner and I are moving in together. He is selling his house to move into mine. Both mid 40s and been together for 4 years. He spends 5/6 days at mine so makes sense. Both houses are similar 3 bedroom size.

With his equity he can pay off my mortgage and living mortgage free is attractive.

We are not arguing over finances, but need to be careful to protect our money if the worst happens. My house is worth £289k with £79k left on mortgage. He will gain enough to pay mortgage off and £5k some extra for repairs, such as finally having a nice garden.

How best to do this? I say we protect our assets with stating we get our contribution back then spilt equity. He says that he owns 30% and me the rest.

What’s best?