My machine has a central wicking system and a bath for the bottom end but, for adding a drop here and there, I really like this 50 or 60-year-old PFAFF bottle.
There is nothing special about the bottle itself, but at the base of the spout is a wee bit of open-cell foam. This allows you to squeeze out one drop at a time. I have also used needle oilers and they are pretty good, but I like this one better. Maybe just because it is old.
As for oil I just use a good, basic sewing machine oil. Juki says I should be using their Defrix oil, but what I have is regular SM oil and comes in a quart bottle labelled "Sewing Machine Oil". Honestly, I think this stuff is just ordinary mineral oil, paraffin oil, baby oil with no smell. Even though I have a whole shelf full of lotions and potions, I don't get too spun up on the machine's oil beyon that it be decent quality, clean, and appropriately applied.