I'd be worried about a 6-month old in a hammock, they tend to roll you up and that's bad for an unattended baby. I wouldn't be able to sleep. Ditto the dog bed, that's way too soft for a 6 month old- crib mattresses have to be a certain hardness. I'm not trying to go all nanny state on you, but I've just been through all this and less and less is acceptable- even those side positioners and bumpers from a few years ago are out. http://mom.me/parenting/5823-when-can-i ... ld-pillow/
Have you looked at a co-sleeper? Arm's Reach are the ones we had, they have a small footprint (if you get the small one) and the side comes down, or doesn't depending on your need. There are some fairly nice ones on craigslist usually, and they're safer than DIY.
Have to applaud you though, I've only just test fitted the car seats in the van and my girls are almost two. I might have a shred of sanity left if I'd been able to get out in the last few years.