Hey Guest! Ever feel like entering a Game Jam, but the time limit is always too much pressure? We get it... You lead a hectic life and dedicating 3 whole days to make a game just doesn't work for you! So, why not enter the GMC SLOW JAM? Take your time! Kick back and make your game over 4 months! Interested? Then just click here!
I second PyxelEdit. It's exactly what you're after.
Start with some videos and some simple tileset to see how its workflow works and how you can tile a "fake" level to see it update as you update the tiles. Before moving onto the 47-tile set.
ProMotion NG has a tilemap mode with extensive features. Arguably the "Photoshop" of pixel art editors.
In tile mode draw your graphics (no matter what size) and tile sets are automatically generated. It even optimizes your tilesets for mirrored tiles if need be. Very comfortable editing for any type of pixel art.
Tile map drawing and testing is seamless in ProMotion: draw tiles, see them updated in the tile library.
1.) I make templates based on a 128 x 128 scale in Photoshop (128 x 256) (256 x 256) (256 x 512) etc..
2.) I import said template into Affinity Photo (iPad Pro w/ Apple Pencil).
3.) I finalize in Photoshop (iMac), and then turn the drawing into a titleset.