Many of us have used kettlebells in the past for strength training. Soft kettlebells are worth a look if you are worried about damaging the floor or suffering unnecessary injury. Valor Fitness SKB Soft Kettlebells can be what you need. They come in 10lb, 15lb, 20lb, 25lb, 30lb and 35lb sizes.
These kettlebells have a flat bottom and easy-to-grip handles. Cost as low as $31 depending on the version you pick.