Do you have a doll with no legs, or the wrong legs for your purposes? Or do you want a doll posed without a visible stand?
A toilet paper roll core makes a good skirt base and/or stand.
Cut a piece of paper to fit around the toilet paper core. Glue if you wish; I usually just tape it.
Tuck both ends inside as smoothly as you can. Doesn't have to be perfect.
Measure another piece of paper to fit the exact length and roll it up rather firmly and slip it inside; tape in place. You now have a smooth surface inside and out on which to glue petticoat or skirt fabric. This is especially important if your fabric is on the sheer side.
I measure so that the length is correct whether I want the skirt to begin under the bosom or at the waistline and then taper in the sides as needed,
,,, keeping in mind the line of the dress I am fashioning.
I just use tape to hold the sides together and keep it a bit longer than I think I will need until I know for sure.
If it is Empire styled or fits just under the bosom like this Edwardian skirt, before I glue in place under her bosom I trim off any excess FROM THE TOP (so that you have a smoothly finished bottom) and fit the sides again. Sometimes I glue on the petticoat or dress fabric before I make the bodice, sometimes not. It all depends on the style and whether there are belts or other trim around the waist, etc.
Here I used a toilet paper roll as a stand for Grandmother Matamosca, who had a Dollar Tree skeleton as her body and at that time I did not have the means to make her stand upright. I made her complete dress then dropped her into the cut-down roll and let her tip forward at the waist and she looked just like a stooped old lady.
Generally, though, if I am using the roll as a stand, I tape and glue it at the appropriate spot on the hips. I usually glue a line of lace inside the roll in case someone decides to pick up the doll and look under her skirts (and you know people do that).
If she has no legs at all, I cut a circle of either white or the dress fabric and glue over the end and up the sides, then I make her skirts long enough to puddle around her slightly on the floor. If someone picks her up and looks underneath, all they will see is a nicely finished bottom.
I have made a skirt with only one layer of fabric over the base, as well as some with multiple layers, including a petticoat, an underskirt and overskirt, etc.
Another thing I recall doing with one of my smaller doll torsos was that I wound up cutting a slit through one tube, flattening it out and removing some excess on either side, so basically I wound up with a flattened curved piece that I shaped further at the butstline and retaped. I think I may still have a pattern somewhere that I drew when I was working with those smaller dolls.
This process is probably not original with me, I am sure; it is just how I do it.