The Ultimate Guide to Sex and Disability is where I usually begin when I need information on sex and disability. Its like 300 something pages of information on how to create an empowered sex life for people living with disability, pain, or chronic illness. I recommended this book to the woman who called because it covers sex positions that minimize stress, how to manage fatigue and pain during sex, and how to adapt sex toys. It also has a pretty comprehensive resource section. It's definitely a must for any sex library.
The sex props we usually carry are the Jazz Mini, Wedge, and Ramp. These three are all wedges of different angles and sizes. They help support and angle hips, heads, thighs, and any other body part that could use a strategic lift. They are also great used in combination. We also carry the Wing, which holds a vibrator or dildo in place hands-free.
Many people with mobility or fatigue issues also find sex swings and slings to be useful. They take weight off of your body and allow for more movement with your partner. Our G-Spot Cuffs and Doggy Rider are simple types of sex slings that can help support legs and hips. I found some pretty crafty instructions on how to make your own full swing here. Swings are also pretty damn hot. Most of the ones I have seen for sale tend to be on the expensive side, but for some people it's more than worth the splurge.
It's also a good idea to check out products that are not made specifically for sex. Yoga bolsters, straps, and cushions are particularly useful because they are designed to help you comfortably position your body, come in high quality materials, and are often less expensive than their explicitly sexual counterparts.
Please leave any more ideas or suggestions that have worked for you in the comments!