For people thinking there's not enough bombs to kill the monsters, it's fine. All you have to do is enter the shop (by clicking on "Shop") and then exit the shop and your bombs are instantly refilled. But entering/exiting shop does not respawn monsters. So you could do this even with very minimal bomb upgrades if you want.
I guess dying respawns monsters? Then don't die. It's really not that hard.
The only difficulty in the game is right at the start, when you can't see in front of your face. So first thing to do is improve the view, then a treasure upgrade, then bomb upgrade, then you probably want to save up for another treasure upgrade (or a speed upgrade) and so on. When an enemy is on your tail, just drop a bomb and take a few steps away easy peasy.