I flatten, thickness and smooth all my board by hand. For smaller boards it's very fast, for larger boards its gets a bit demanding on your stock of elbow grease. The only real hard thing I find is thicknessing multiple boards to the same thickness, this is time consuming and hard to gett it all to the same thinkness while keeping the faces nice parallel to each other. For this reason I'm going to buy a thickness planer, but only a thickness planer.
I have a Staney no 6 type 15 setup with a deep cambered blade for initial rough flattening, a Stanley no 8 type 11 with a cambered blade for final flattening and edge jointing and a Staney no 5 type 10 with a slight cambered blade for smoothing. All blanes have a Hock blade and chipbracker which hugely improves the finish performance and easy of use. (the original blades and chipbrackers are kept wrapped up in oily paper)
Edit:: I used to buy planed wood from the DIY stores many many years ago, until I found out I was paying a very high price for very poor quality with a lot of incosistant thickness and with cup and bow and had liuttle choice in timber species. Then I switched to the local timber yard who offer to either get the wood rough or finished to specified dementions. I was wrapped, but often found that boards where still a bit cupped and bowed, sometimes had burnmarks. One day I found out this was because they took the rough boards from outside storage, run them through a thciknesser both sides without any support to prevent the ends of long baords sagging down towards the floar, manually forcing them throughbevause the board other wise got stuck in the machine because of the too have cut. I now buy from another yard who will also finish boards for you (takes a few weeks before the boards are ready). You receive the wood nicely aclimated, flattened, thicknessed and packaged but at premium price. So I buy it rough. Lower price, faster at home and the freedom of grain selecteion at any stage.