Baseball sliding shorts also work pretty well, and you can get them in most sports stores. Another approach is to put pads inside a pair of bicycle shorts. With these, the outer pants can move some, but the undergarment stays put and protects you. You can buy shorts made for hockey or aggressive skating, or sew pockets and pads inside any loose pair of shorts. Sometimes when I'm downhill training, I wear padded outer shorts over padded underwear.
Hands are fragile, essential to our lives, and prone to injury in crashes.
I've been wearing full weight hockey gloves in most of my high-speed crashes and have never had a serious injury with them. They protect against wrist injuries, thumb injuries, abrasions, and pretty much anything else that could happen to the hand. They're hot and heavy, but you can easily take them off when you stop for a break. For gentler skating, standard wrist guards should be worn at all times. Elbow pads need to stay put when you slide, too, so be sure they have sturdy straps and a snug fit.