How to paint a "wavy" ceiling and leave no patches!

I Am renovating 70s built house that has some rooms with "wavy" ceilings. How can I best paint them to get a nice flat even finish?! Originally they have darkish magnolia which seemed to hide the problem. I did make mistake of using medium roller to put on 2 coats of Dulux Matt emulsion but then saw the problem. The ceiling isn't flat but has "wavy" sections. So I did a coat with a longer pile roller and it looks better though not as good as I hoped. Do just need to do yet another coat with longer pile roller or am I missing a bit of preparation work or using a different base coat paint to even out the ceiling? Help much appreciated as paint expensive! I don't want a polyripple or rated type textured ceiling.