When I switched from mobile to PC, I ran into an infested floor on floor 11. Green slimes and bugs killed me. I’d been playing on mobile for over a year. I totally feel your pain.
One thing to consider is food. You’ll need a lot as you learn to navigate combat. As soon as your health hits yellow, eat food. The game will pause when you eat, so chow down in the middle of a bug swarm if you need to. Salmon berries, forage, spring onions, and blackberries are a plentiful free source of energy. Parsnips in spring and hops and radishes in summer work well as energy sources too.
A great source of energy is high quality chubs. If you can fish, keep all of your chubs. I like to store them in chest at the top of the mines.
Check your crafting menu. If you can make cherry bombs (and with 30 copper bars I suspect you can) and staircases, it will really make your life easier.
Also, embrace infested floors. I finally progressed in combat when I hit that infested floor 11. I died, reset the day and tried again. After dying and restarting the day multiple times I was able to kill all the monsters. Finally, I could descend the mines.
I hope this helps! Good luck!