Personally when it comes to matryoshka designs, I really like the idea of them being jumpsuits. But seeing as I'm sure you are already using a sweatshirt, then matching green sweat pants would give the idea of it being a jump suit.
Some other ideas could just be some plain colored jeans. Because keep in mind that the video for that song is all about bright, solid colors (I would suggest red or yellow).
For the shoes I would say ankle boots or converse in some solid, wacky color.
Rose Lalonde - Homestuck - [god tier] - revamp
Dirk Strider - Homestuck - [god tier] - WIP - [dreamer] - WIP