I'd recommend a roman chair if your problem is muscular. I spent $300 for a really nice one and my lower back pain has been a thing of the past for about a year (they can be had cheaply too). Careful squats and ab work also help tremendously.
DMing at home has it's advantages, huh? Well, I know you're a guy who does a fair amount of winging it, but I would put all my planned encounters (and then plenty of contingency encounters/npcs) on encounter cards/notecards all statted up. I'd bring the PHB + DMG + any minis previously handpicked and in a baggie (corresponding with the cards) + 1 set of dice. Alternatively, you could use Kenzer's 3.5 screen in lieu of the PHB + DMG. Lord knows every chart in all of creation is on that beast. The thing's amazing! Finally, insist that players who play non-core classes provide the splatbook or at least a printout of that class.
I also heard some kook made a spreadsheet with monster stats ...