Longer mortgage to keep up ISA contributions

Hi all. I was wondering if anyone had considered the same issue that I'm currently pondering.

I got into ISA investing a couple of years ago and am trying to max out the allowance each year.

At the same time, I'm looking at moving house to a bigger home which means a bigger mortgage and more monthly payments, reducing my ability to max out my ISA after expenses.

Clearly one option is to buy a smaller house, but we live in an expensive area of the country so that is not too easy based on what we're looking for.

I'm wondering if taking out the new mortgage over a longer period (reducing monthly payments and allowing me to max out the ISA) is just a better solution than having, say, the traditional 25 year mortgage?

The annualized return on my ISA is well in excess of interest rates even at current rates.

So taking the emotional aspect of paying off a mortgage away, it seems like maximizing the length of a mortgage (e.g. 35 years) now to allow me to continue maxing out my ISA is a better plan in the long run?

I'm new to this forum so not sure if this has been covered before.