A good option is to get the 30 year then pay more on the principle with the goal of getting it paid down in 15 years, but allowing “wiggle room” in case some months - or years - are tighter financially than others and you could just pay at the 30 year rate those months that you need to.
My general advice for a mortgage is never to prepay but unless you’re paying off the entire balance. Instead, take the extra money you would have used for the prepayments and put it aside. Build up a parallel investment fund with that money until you get to the point where your investment fund exceeds the balance on the mortgage. It will take years, but if you’re disciplined enough you will be able to pay off your mortgage while maintaining a LOT of flexibility in your finances.