You have two types of problem, when you cum you feel a pain, that usually happens when you have excessive masturbation or dry/hard masturbation. reduce the occasion, enjoy fully.
Of course a natural pussy is a better option as it gives right pressure on right places.
On your using oil, I dont think that's a good option. Specially Japani Oil, if a known garbage, people buy for nothing. Dont use coconut oil as it contains liquid parafin. Dont use Mastard oil as it adds chilli powder. I can suggest only one thing, use good quality Honey. This has been used for long.
In old age, they used to make a mixture of cow's urine with burned lotus leaf, rock salt and buffalo milk. I dont know the reason, but look at it, these are all natural products.
So try honey and do say if it works. Before that, ofcourse dont have a dry handjob or pressured handjob.