There are several ways to go. None of them are complicated, but it does take some thinking things through. In our family I've setup bikes (all are triples and have 68mm bb shell widths) with the following combinations:
50/40/30, 11-34; 48/36/26,11-34, 110mm bb; 46/36/26(can take a 24, 8 speed), 12-34, 107mm bb; (2)44/32/22, 11-34 103mm bb; 44/32/22 Shimano Octalink bb on Cannondale T800 (real challenge); 50/42/30, 11-32. I've also tried some other combinations, but did not keep them on the bikes very long.
In all cases I changed out the rear derailleur to a Shimano Deore or LX. Tiagra front derailleurs are really flexible and work well with all those combinations. All use Shimano STI shifters ranging from Sora to 105's. All are 9 speeds except one (my favorite and the one I ride every day). If you have a short cage, double, rear derailleur, you will need to change it , and you might as well go mtn bike RD at that time. I tried an 11-30 rear cassette with a long cage 105 RD and could not make it work very well.
If you use the "trekking "cranks the bb axle is the same size as used for "road" cranks. If you go for a mtn bike crank set a shorter bottom bracket is needed. The 8 Speed went from a 115 to a 107mm, and the 44/32/22 setup went from a 110 to a 103. It seems like it takes about 7mm difference to maintain a 45-47mm chainline.
One way to figure out your bb size is to get the cranks you want to use. Install them on the present bb, and then measure your chainline. About a 45mm works well for road/touring bikes. Take the difference from what you have to what you need and order appropriate size bb. Check out the Park Tool website for chainline measuring advice.
44/32/22 on LHT. I'm just building this up now, and used the crankset from the Volpe(below)
46/36/26 on Trek 1000. My every-day bike.
44/32/22 on Bianchi Volpe. This crank is now replaced with the original 48/36/26 crankset.
On the 46 -12 combination I spin out at about 28 mph at 90 rpm. With the 44-11 it is about 26 mph at 90 rpm. How fast do you want to go on your commute?