Helping my parents

Hi MSE Forum-ers,

Long time reader, first time poster.

My parents now need a little financial help. They would provide an 80% deposit and I would pay the remainder through a mortgage. Deeds would be in my name.

I can afford the payments (would be 40% of my savings per month, after all commitments and discretionary spending, could boost to 33% if that made a real difference [25% max])

My questions are.
1) What product am I looking for? (its not a mortgage for my primary home)
2) How do I find out the affordability criteria?

My mortgage is at a great SVR and I don't want to negotiate (we pay the pre-SVR amount which is where some of the savings would come from)

Thanks for you ideas,
Jo C