I know what you mean about floating in space, but there's no foreground detail by his feet, so it pretty much looks like he's floating in space, sans the stars.
If you want it to look more grounded, look into grey or white seamless.
Awesome job with the natural light (thats all I use as well). I understand the whole floating thing but try not to use loose fabric, look into seamless paper, its gorgeous and it'll give you the effect your looking for while looking more professional
I do have seamless paper, white......but it's a pain in the you-know-what without a stand, and I'm too cheap to buy a stand The muslin is so much easier! haha.
I figured. I saw the shirt at Target this week, too. My 3yo wanted it....
I actually prefer simpler clothing with no bright patterns or logos for little and big people in general; I'm kind of a minimalist when it comes to that sort of thing, but that's just personal preference.