Just a follow up to this. I spent a lot of money on different a* solutions, and the best, by far, was
http://arongranberg.com/astar/ .
There's a free version, but I opted for the pro versions ($100) as I'll be able to apply it to more situations (both 3d, and 2d).
The latest version of A* works with BoxCollider2D which is perfect! However, there's 1 downfall. When you create a tilemap with TK2D it create it's colliders using EdgeCollider2D. It uses EdgeCollider2D as it reduces the amount of PolygonCollider/BoxColliders needed. So basically you need to manually draw all the BoxCollider2D's for each 'solid' tile, then get the A* to generate a grid.
If your tilemaps have a consistent tilesize (32x32 64x64, etc) and each tile is either collidable, or not, then you can use my super handy UnityEditor plugin to automatically loop through your tilemap and place a BoxCollider2D in it's place.
https://github.com/kevdotbadger/BoxColliderGenerator