To live a simple life means living below your means.
A few ways to live below your means and live a simple life are.
Buy less house than you can afford.
When purchasing a house never go for the most expensive one.
Buy a house that you can reasonably afford and pay off as soon as possible. Try to pay off your mortgage in 5 or 10 years vs 30 year mortgage.
The sooner you pay your mortgage off the less you will pay in interest to the bank.
Only buy something if you really need it.
People living a simple life will decide if they can do without something or not. It's okay to buy things that you want. But if you want to save money you should think whether you need that item or not.