I've searched this sub a ton but never found the exact answer to this, so here goes:

My partner and I plan to buy a house in the next 3-5 years to live in. It will take us probably two years to save the deposit. In the meantime, I'd like to start investing in a S&S ISA to work towards retiring early; I estimate I'll be able to retire in 10-15 years if I start investing a substantial amount of my salary now.

But which is better, financially? With compounding, is it better to get the ISA set up for retirement sooner and buy the house only in our last couple years before retirement, renting in the meantime? Having a mortgage sooner obviously means we're debt-free sooner with our main living expense gone after x years, and it means we're investing in property as well as the ISA, but it also means a few years more full time work. And I don't know if it really counts as 'investing in property' if we're planning to live there as our family home for the long term without renting out or moving. Does it depend more on my priorities, or is there a more objective/mathematical answer to this question? I've found a lot of discussion but it's mostly on comparing the ISA with a buy-to-let; this would be our personal home.

Thanks in advance!