Microsoft is still offering to convert your Gold to Game Pass Ultimate for $1 and then $15 per month after it ends. It used to be that you could not add a Gold subscription to an existing one, but Microsoft had changed it allowed players to stack up to three years.
So here’s the easiest way I can think of to do it:
I waited for my Gold to run out and I only added one year, but you can add more. You can redeem your gold memberships at redeem.microsoft.com. You will need to make sure to uncheck the autorenewal each time. I have heard that it can add a month to your 12-month membership making it impossible to use your final 12-month membership.
Once you are loaded up with 36 months, you can head over to the subscriptions section on your Xbox and choose Game Pass Ultimate for $1. At that point, you will have 36 months of Microsoft’s Game Pass, a $359 value.