Silicon heats compound substitute
I think some kind of compound is neccesary, but there are 2 substitutes for silicon heat sink compound.
There is a non silicon compound available from mg chemicals and others. Advantages are no migration or component contamination.
There is also a silicon rubber I have seen. It is a thin rubber grey sheet used in place of mica with silicon. Electrical insulator but high heat transfer. I have not been able to buy them but have seen them used a lot
That said I prefer silicon because it is lower cost and I believe works better, as well as silicon is easy to see where it is, and also to see if it has dried out