Simply adjusting the seat can make a big difference in comfort, though I'll admit that some seats (saddles, whatever) will be uncomfortable no matter what you do.
Tweaking where the shifters and brake levers are and how they are angled is something worth doing as well.
For what it's worth, your bike appears to have had the cables and housing cut on the long side coming off the bars so if you decide to go with a taller stem and/or riser bars at any point, you shouldn't even have to redo any of the cabling. A handful of hex bolts and you're ready to roll.