Troubleshooting my first sourdough loaf

Hello fellow bakers! I've baked a few sourdough loafs in the past without much success and I'm getting back to it now that I have a better oven and bigger kitchen 🙂 My first loaf was delicious, but I am not 100% happy with the crumb.. I hope you can help me improve it.

This was my process:

• I used the strongest flour I could find in the supermarket here in Spain. It says 13% protein and W > 300
• My starter is relatively new, only a week old, but it is already rising nicely and more than doubling in size every time. I used it at its peak
• I started in the morning, mixed everything and aimed for ~70% hydration (difficult to tell because I don't have a scale yet)
• I performed 4 sets of stretches and folds and overall. From mixing until shaping and putting in the fridge the total fermentation time was around 8h-9h
• The temperature here was very warm. Outside was over 30˚C, so in the kitchen it mush have been 25˚C-ish
• Rested in the fridge overnight and then baked the next morning
• When removing the dough from the banneton, it stuck badly and I had to be a bit rough with it to get it out

The oven spring was moderate, with a decent ear and the crust was really crusty and flavourful. But the loaf felt very heavy for its size and the crumb slightly gummy. Those large holes also make me think something was not exactly right, but I don't know what!

Can anyone give me some pointers on what to try next? I really appreciate it :)