Firstly, congrats
Here's a couple of thoughts from my recent experience (19 week old twins).
- sound leakage in our house seems to come from under and around the door rather than through the walls, some form of draft proofing may be a much cheaper and most effective solution - have a listen in the room and then block up the bottom of the door with a towel and see if it helps.
- ours seem to only be really sound sensitive when first going to sleep, but once asleep are fine and we don't bother much about noise. In my view, it's probably a good idea to get them used to some noise or you're fecked if you go anywhere else, like visiting relatives for example. Maybe limit the noise level when they first go down and then go back to a normal volume. Creeping around all the time is annoying for you and sets up problems for the future.
- on the positive side, you're in a bungalow so don't have to worry about neighbours, ours have been very patient and we've been lucky, but friends of ours have had "words" from their unsympathetic neighbours