2.1 isn't difficult at all.
Start out with a pair of mains you can live and grow with. That takes care of the "2" part.
When I say to grow with, I mean those that offer a matching center speaker. But, be aware that there may be a time limit whereby that matching center may no longer be available new.
Now, choose the best sub you can afford. Look for one with the most flexible setup options and, most important for your current setup, one with two line level inputs. You can't combine two stereo channels into one subwoofer input.
Likewise, speaker level inputs are pretty standard and may be useful depending on your chosen receiver/amp.
As far as the amp/receiver goes, if you follow the above advice you'l be pretty welll set for anything you choose.
You indicate that you are going two channel so I'l assume a two channel receiver. If possible, go for one that has a preamp output or, even though it's not too common, a subwoofer output. This will allow you to use the crossover on the sub to determine and set the optimum low pass point for your system. If worse comes to worst, you can always use the sub's speaker level inputs and some people swear by these.
Of course, if you go for a multi channel HT receiver, you'll have a LFE output and that will simplify your life somewhat. You'll have to read the manual to see how to integrate the sub into the picture.