Yes I have even built altimeters for my rockets but Baro pressure is only good to about 42,000 MSL. Our flight computer also has an accelerometer which we can add to steps to the baro and get good accuracy to about 67,000 feet but it only works good in something that moves fast like a rocket so right now GPS is the only way to go that I can think of.
I have a friend that has an older GPS that he launched on a balloon to 84,000 with very good accuracy (before they started locking the altitude to 60k). The newer ones are just locked out so you can’t use them for guidance of say a destructive device, but GPS is accurate up much higher than 100,000 feet. You just have to be able to unlock them with a manufactures code or hack it somehow. The 60k is a number some government picked because all GPS’s seem to be capped at 60K.