For 24" deep base cabinets, you want the 21" tandem blumotion slides. If you're using existing cabinets, I strongly suggest having some production drawer shop make up all new drawer boxes to go with the slides, as they won't fit onto your original boxes. The Blumotion slides require only a 3/16" gap between the sides of the box and the inside of the cabinet opening, and the slide model depends on the drawer thickness and whatever vertical adjustments you want. 563H is the model I used recently on my kitchen and vanities. You don't need anything to attach to the back of the cabinet.