There are alchemists you can buy ingredients from, yes. The trick is knowing who has what, i.e. look it up so you don't waste your time hopping around the map.
You should have all your most used potions hotkeyed, but it does get annoying to pot up and oil your blade every other encounter. That's as involved as you want it to be, though for humans and the strongest monster fights, you should probably apply the correct oils at the very least.
The most powerful build (Euphoria) is coincidentally set up the way that you don't have to re-apply oils, or drink potions every other fight, because they end up lasting upwards of an hour. Probably intentional, now that I think about it.