We have a baby on the way and the location of the baby's room is much too close to the living room of our home... which means that if we have a light-sleeping baby, we will have a problem with sound (primarily talking and even low-volume television) making its way into the baby's room.

We figure that step #1 in solving this problem is to replace our "vintage" 1959 hollow-core doors with something that provides good sound insulation; much of the sound seems to seep into the baby's room through the hollow-core door. So I have a few questions:

a) Who makes the best quality solid-core or solid-wood door for purposes of sound deadening? Note that I probably don't need to replace the framing, but just the door. And note that this is for RESIDENTIAL applications, so I'm looking for something attractive for that purpose (i.e. a craftsman-style 3- or 5-panel door, or even a traditional 6-panel colonial-style door).

b) In order to improve the sound-deadening qualities of the door even more, do I need to build a threshhold under the door? Right now the hardwood floors simply flow into the bedroom from the hallway with no threshhold, so sound can travel underneath the door. I assume this is an important sound-deadening step, but having never replaced doors before I just don't know?

c) Do I have to buy solid wood doors in order to get maximum sound control... or is there such a thing as a solid-core door built from other materials (that might be better for sound insulation and/or less expensive)?

d) Any other suggestions would be helpful. Thanks!