K.E.
For Christmas trees I would recommend you try Garden Ridge. They have a variety of sizes, ranging from 4 ft to 12 ft and they are the least expensive I've found. They also have really pretty plastic globe ornaments that look just like the traditional glass ones and they won't shatter into a million pieces if someone accidently knocks one off the tree. We bought a 4 ft tree and placed it on a table in the corner so my one year old wouldn't pull all the ornaments off!
As far as an appropriate gift for a 6 month old, someone bought our son a Discovery Ball when he was that age. It doesn't look like much(a large ball attatched to a base that spins and sings the alphabet) but my son absolutely loved it and it helped him with strengthening those stomach muscles. You can find them at Walmart.
By the way, I am also a stay at home mommy with a young child. I'd love to chat sometime!