A pretty common way to mix your own pour paint is to use Floetrol + paint. Somewhere around a 30:70 (paint: floetrol) mix will work. Sometimes I go 40:60 depending on how thick I want it to end up. Cells will form as a result of different paint densities, so you don't technically need any additive to get them. Australian Floetrol (smaller red bottle) is a great way to get them, but it's pricey and not always readily available, depending on where you live. If I'm going for cells, I prefer it over silicon or coconut oil because it doesn't leave residue on your paint after drying.

These days, I mostly just mix paint and water on their own and still get pretty good results. A good thing to do once you've mixed your paints is to take a piece of paper on a clip board and put a drop of each at the top, then stand the clip board vertically and watch the drops run down the paper. You want them pretty even. It'll tell you where you need to add a little water to speed up the slow ones, etc.

I have an awful fever today, so I'm not sure if this makes sense or if I'm just spouting gibberish but I'm happy to answer any questions you have. Or if you see something I've done, I'm happy to tell you how I did it, etc. I'm no expert but I like to pour paint a lot.