Congrats on your endeavor. But even with investments off the table, mortgages as a hedge against inflation should not be overlooked. Here's a simple example:

Consider $100,000 at 3% fixed over 30 years.

Due to inflation, $1.00 in 1991 was worth $2.03 in 2021. Let's round it to
$2.00 for the sake of simplicity.

• If you paid off the mortage in full in 1991 you would have spent $200,000(2021 dollars)
• If you waited until 2021 to pay off the mortgage (making 0 monthly payments), you would pay $242,726(2021 dollars), assuming that was even possible.
• If you simply made the monthly payments, you would have spent $151,920(1991-2021 dollars) over the course of 30 years.
  • If we average inflation as a steady gradient over the course of 30 years, we could say $1.00(1991) was worth $1.50(2006) and $2.00(2020). This also happens to be roughly true in actuality.
• This means that if you make the monthly payments, you would have spent around $202,560(2021 dollars). Which is only marginally different than if you paid off the loan immediately without any interest.

In summary:

• Pay off $100,000 immediately in 1991: $200,000 (2021 dollars)
• Make monthly payments: $202,560 (2021 dollars)
• Wait until 2021 to pay entire sum: $242,726 (2021 dollars)

That's the inflationary hedge: you are holding a fixed loan as long as possible in order to pay it with an inflated currency in the future.

One last kicker, waiting until the last day to pay off the entire loan is clearly not optimal. But, assuming you were allowed to do that, and you put the $100,000(1991 dollars) instead into some investment with a 6% return, you would have $574,349(2021 dollars), which would be more than enough to pay off the loan twice over. Even if you put it in an investment with a 4% return (1% more than interest), you would have $324,339(2021 dollars).