beginning to design levels for a hand drawn game, not sure which way to go

Hey guys. I've been working on a game for the past couple years called "Project: Rudra." Rather than go into details, you can learn more about it here: http://patreon.com/hybridmink Basically it's a 2D action platformer. I decided to go with tiles rather than placing art over collision so that I can adapt levels down the road and have breakable walls that fit seemlessly into the environment. I've drawn some tiles for the first level, but getting the art to tile perfectly with things like slopes and edges will often have some kind of issue. It works for the most part but I'm wondering what the best approach for this type of game would be.

I'm an artist/animator working with a single programmer right now. The game's being designed in Unity. If anyone has some advice or general info on designing 2D levels in Unity, let me know! If you check out the link above, you can see the art style I'm going with in the character animations. Hopefully this was the right place to post this.