Everyone in our office has an Aeron chair and back problems are way down. It's an awesome fit and forces your back to be supported while you sit (*you must sit correctly in the chair - if you tend to teeter on the front part of the seat, you can feel the alignment in your back go out of whack).
Also, you don't want your chair to be too high, like you're towering over the keyboard. And your monitor should be in a position where your eyes are looking down somewhat as opposed to having to raise your chin/head to look at the monitor. This raising of the head/chin will also make your alignment go off a bit and create low back problems.
For the immediate relief, there is this stuff called Bio-Freeze - I buy the one with the roller - and instead of having to mess with an ice pack, you just roll this stuff on and it works just like an ice pack - ice is better for muscle strain than heat within the first 48 hours. A foot rest is helpfl for some, but I have found that I never get it to sit right and it causes me back pain anyway, so I just adjusted my seat so my feet can be firmly planted on the floor. Also, unless your back is 'out' and needs an adjustment, some gentle toe touching type of stretches would help that area a lot. Or, there is the pelvic tilt, which is my personal favorite for that low back area. You lie flat on a firm surface (the floor on a yoga mat is ideal), you can bend your knees slightly so as not to strain the area, and you gently pull your pelvic area down the floor, so it's flat against the floor and hold for 10 seconds, relax, repeat. My very first chiro taught me that when I was preggo with easy child and my back went out. It is a great little exercise to take pressure and pain from your low back.