Making your own crinoline is easy---the materials are inexpensive and readily available at any fabric store. Since very little (if any) is meant to show, you don't have to be an expert seamstress either. If you intend for the bottom of the crinoline to show beneath your poodle skirt, you can have fun with the colour of the tulle; try something other than white for an unexpected flair.
Measure your waist with a tape measure, and add 2.5 cm (1 inch) for the waistband overlap. Cut a strip of 2.5-cm (1-inch) wide ribbon to this measurement.
Cut a square of Velcro or other burr-fastener tape that's 2.5 cm (1 inch) long by 2.5 cm (1 inch) wide. Note that the tape is made up of two sides: one with tiny, pointy hooks and one with soft, raised loops.
Use a needle and thread to sew the pointy hook side of the tape to the underside of the left end of your ribbon.
Sew the other side of the tape square to the top side of the right end of your ribbon. Be sure that when placed around your waist, the two sides of the tape "grab" each other and hold the waistband in place.
Use your waist measurement (including the inch added for waistband overlap) to determine how much tulle to buy. The more layers of tulle you sew to your waistband, the fluffier your crinoline will be. If you want five layers of tulle, for example, multiply your waist measurement by five and divide by 100 (the number of centimetres in a metre). The result is the number of metres of tulle you'll need to buy for five layers.
Cut the tulle into strips that are each as long as your waistband.
Sew the crinoline
Stack your layers of tulle, and pin them to the bottom of your waistband using straight sewing pins.
Sew the tulle onto the waistband. Don't worry about your stitches being neat or clean---they won't show. You just need to make sure each layer is attached to the waistband.
Trim the bottom of your crinoline to the desired length. It's up to you whether it peeks out from the bottom of your poodle skirt.