If you choose to buy a house it won't be in your name. Therefore put your name on the lease, if done for a period of 30 years, you have the right to live there and it prevents the owner selling the title deed from under you.

John, I am waiting to travel to Thailand also. It's no use thinking of travelling in the near future. Thailand is way behind in tackling covid19. I estimate two years before unrestricted travel is possible to Thailand. You will need Visa's, a ninety day visa to go out there on then after 60 days go to thai immigration and apply for an extension for a year. You'll need money in a thai bank, £20,000, or approximately £1650 per month going into your thai bank account. The best and only place to ask is the thai embassy. Give them a call.

What does the lease agreement actually mean. Does it give you the sole right to live in the property if the relationship fails or your both still living there?. Does it mean that you have the sole right and she needs to find alternative accommodation.?

I think it refers to where you are staying in Thailand. And name and address of person you are meeting in Thailand .