A-line slip recommendations

Amazon or ebay! They have loads that are just tulle, and very reasonably priced!

That's what I was looking at was worried about them not working out.

I really depends how much ... stiffness? Boof? you want under the skirt? Plus how heavy the fabric over the petticoat is likely to be! If you have a heavy skirt, that will weigh down a tulle-only petticoat a lot more than one with hoops in it. But generally, tulle is pretty stiff and should work just fine, it will just have less volume than a hoop will have.

I did find some threads mentioning this topic, which do have photos, here and here of dresses with nothing and with a hoop, but they don't show a hooped petticoat vs just a tulle petticoat.