Your partner also needs to protect themself somehow, in that should you split up years down the line, you will have a house, and your partner won't, and more than that, given the inexorable rise in house prices, probably won't be able to afford to buy one either.
Your partner needs to seriously consider buying a buy to let, now. Your partner maintains and improves that, and you maintain and improve the house you both live in.
Failing that, you both need to see a solicitor and get a 'deed of trust' drawn up, that takes the value of your house now, and states that in the event of your separation, you will pay your partner half of the difference in price between now's price and that future separation date's price, if that makes sense? And then you both pay for any maintenance/improvements to your house, i.e., the house you live in.
If your partner can't afford a buy to let where you live, then look elsewhere. A cheap terrace anywhere is at least a roof over your partner's head, and some security, should you split up.