Computer chair is a big thing for bag pains, my dad has this chair that after a day of work my back would be destroyed. I have two chairs in my office, one is a exercise ball that I use once in a while and the other is a basic char that only had lumbar support, both cheap and both work great.

Drop sets are amazing for putting on mass, I would give them a try if you can. Your break should only be the time it takes you to lower the weight.