Underworks is definitely a good place. However, if you're not straight up-and-down (if you have a couple extra curves in the torso area), I'd recommend the cotton concealer T and muscle T. I tried the double compression one, but as I'm a bit overweight, it didn't quite do the job.
As far as packing, there are a million places online. You can get packers for everyday comfort, for using with a partner, or for urination. Rather than give you a list of sites like the ones I've used, check out
http://www.ftmguide.org/. This is by far the most useful and informative site I've found for anything ftm. Just a little tip on the STP packers: these little guys use medicine spoons for piss-catchers, and they can be insanely tricky. I bought the one from DJ's, and never got it to work until I took off the spoon and used a silicone funnel. Otherwise, get ready to have all your pants smell like a urinal (tends to make you pee down your legs).
Hope this helps.
D