I have been doing some rearranging in J's bedroom (see the initial setup here). Now that he's older, we raised his bed higher by putting his boxsprings back on his bed frame.
Here's what it looked like before:
And here it is after:
I covered the boxsprings with a mattress pad and a fitted black sheet. The blue quilt is from Target, and the colorful duvet cover and sham are from IKEA.
The quilt is not very thick, but I think it would work well as a single layer during the summer or underneath a duvet for the winter. I like the washability of the IKEA duvet cover, but the colors are really bright, so I think it looks better folded up at the end of the bed.
I hope to get his room finished soon, so I'll post more pictures then!