Rocket launches from high altitude baloons have been done:

https://en.m.wikipedia.org/wiki/Rockoon

If you mainly care about altitude as with a sounding rocket, it can help quite a bit.

Also some launche loop designs have parts of the structure supported by inflatable members.

And there are even plans for a rather exotic airship design that could be flown to orbit with the help of solar powered electric engines:

https://en.m.wikipedia.org/wiki/JP_Aerospace