Nice game, lovely pixel art! It is a bit challenging for me as well, as others have mentioned. I do wish fires would respawn you with the full 3 hearts, but I understand why you chose to leave it at 1. I never really got used to the jump, it felt a bit off, but not so much as to detract a lot from the game. While I do appreciate the fast deaths and retries, the death might be a tad too fast. Often the game over screen would show up even before I saw the character hit the spikes.
I really enjoyed the temperature mechanic tho, it really did make me go faster at some points. Overall, pretty good, well done! :)