Hi Polly
You will want a dome that will fit the diameter of your breast.
but you want it a little smaller since the suction will try to pull it into the dome.
If its an exact fit, then there will be very little breast inside the dome and it will likely fall off. making it frustrating.
It will be a while before you fill the domes with your new breasts.
I never used the rings I bought, and found that not overdoing the suction or the time will be your best bet.
The nipple issue is a tough one.
Look at the treads from sweet orange. She uses a Pringles can. the bandages have a tendency to fall off. again there is a lot of discussion about the nipple covers in the suction section of the forum.
Yes lots of oil or cream. you want the breast to slide into the dome and not be tugging at the skin. This causes the painful experiences.
The important part is to not put yourself in any pain.
This is a slow process and you will see volume increases before you see and increase in the tape measure.
Try the pump and release or just set the pressure to the max you feel comfortable and then let it off a little.
Try a few techniques and let us know what is working and not.
Also the bosom beauty system has an automatic pump and release system that many girls found easier to use.
Good luck
and happy growing
Bobbi