Congratulations on beating the game with every turtle so far!
Right now, the only "hard mode" is if you choose not to build the tanning rack early on, which disables backpacks, consumables, and footwear. If you are talking about resetting the game and starting over with some kind of prestige points to unlock extra features, we do not have that yet. I'm currently focused on adding more content to the existing normal mode, but we're getting close. Once that's more complete, a prestige system is definitely something I'd love to explore.
Also, I'm really happy you're enjoying this little game so much. Thank you for playing, your support means the world to me :)