Never used cottonseed oil. I used filtered Grapeseed oil for my last experimants along with BA at about 3% and this proved to be completely painless.......I vote for GSO.
Grapeseed is easier to find locally. I was able to find it at Trader Joes. I baked it am home and filtered it into a 10ml bottle. Alleviated painful injections with DECA/PROP/SUS.