Are there apps to split one big screen into multiple spaces?

I'm switching from three smaller screens to one big 42" monitor with Rectangle to emulate multiple monitors. It works great and I enjoy the flexibility in arranging the windows. However one thing missing is separate spaces. I used to have essential apps / documents on one 'main' monitor with others having multiple spaces. Now I have to switch the whole screen and have to go back and forth to find what I need. It's just a minor annoyance but I'm wondering are there apps to remedy this? By splitting one big screen into multiple smaller, virtual screens.