Yes they will get lonely. I personally think you could get away with an established (mature) tank with gravel and live plants if you wanted. In a bare bottom you will pretty much have to do daily water changes; it's a whole lot of work. The most important factor is that when you first get your discus, there can be no active or aggressive fish in the tank and the water has to be clean. I would recommend getting a small shoal of tetras: cardinals, glowlights, ect. The tetras should be in the tank before the discus as they will aid in the discus's feeling of security (if the tetras are out then there must be no danger).
A 29g is a good tank for young fish, so you could probably get 4-5 juvenile discus, wait for a pair or at least two that seem to be buddies and then take all of the discus back besides those two. If you can, however, get a 38g, I personally think they make good discus tanks and you can probably have 3-4 adult discus in them (following the 10g/discus rule, although 4 is pushing that a little). You could also have a small bunch of kuhli loaches for the bottom and a small shoal of 6-8 tetras to add to your discus.
HTH