Best hoop/underskirt for a line?

The fullness of the a-line with be limited by how much fabric is used. For example this is my dress, and even with a bigger hoop, it wouldn't look much fuller as the fabric won't allow for it:

Your best bet is to wait until you decide on a dress before looking for hoops. But if you have seen a bargain and get it now, make sure all 3 hoops are removable and adjustable. That way if you go for a-line you can remove the top hoop (too high for most a-lines) and use the bottom one or two, adjusted to fill the skirt perfectly.

I'e seen loads of 3 hoop ones on ebay with the double layered underskirt....

This is the dress i would be wearing it with....

A two-hoop one would be fine.

I have a two hoop one and it makes my dress above look perfectly full. I only had a petticoat on in that picture, but just wanted to show that I wouldnt be able to fit a mahoosive hoop under it!

MrsT-tobe - I have just bought a 3 hoop off ebay that has fully adjustable and removeable hoops. DuckyBum is right you need to get the dress first. I thought I would need 2 hoops minmum with my dress but it looks best with just the bottom hoop. If your friend is going to lend one to you great but it may not be right for your dress. But then I paid £8 for mine!

This is the best full view shot of my a line dress. I wore a double hoop underneath. A triple was too much and just stretched it kind of.