Earlier, I tried an experiment with running a R410a compressor on a R290 based mixture (ES22a, similar to R433b, the use of it in a R410a compressor being known as the "Davuluri Treatment") in order to avoid overstraining it with high condensing temperatures in my application. But what if you only have a R22 compressor? It turns out you can still do something similar.
Now, R134a probably isn't the best choice since then you'll have to change the oil to POE and discharge temperature would greatly limit the temperature you can achieve. But a hydrocarbon mix intended for replacing R12 or R134a (such as R436a or ES12a) would work well. Hydrocarbons heat less on compression, meaning that a heat pump using it can go to higher temperatures before oil breakdown starts becoming a problem.