You pretty much got your answer to the first part of your question. All else being equal, a heavier firearm will have less perceived recoil than a lighter one.
As far as purchasing a firearm online....
I have purchased several. The two sites I have bought from are http://www.gunsamerica.com and http://www.gunbroker.com.
There is another one that I have seen people mention, but I have never looked at myself. I believe it is http://www.auctionarms.com
There are a bunch of LGS with websites that I have seen great prices and seem to have good reviews from others. (I mainly buy old military rifles online)
Another online option is the CMP. The purpose of the CMP is to distribute old US military rifles to the American public. The prices are great and there is no FFL required (though there are other hoops to jump through). However, if you aren't looking for an M1 Garand or an M1 Carbine, you are pretty much out of luck. Their website is http://www.odcmp.com and click on Sales.
If you buy a firearm through an auction site like GA and Gun Broker, just remember, if it is too good to be true, it probably is. I'd never send someone more money than I can afford to be stolen in any online transaction.