It’s bizarre to me that nowadays an application can become frontmost application at all. When I switched to OSX back in the days, it was an advertised feature that this can’t happen the same way it does on Windows. If something wants attention, its icon bounced in the dock. Nothing more.
Just turn off “Preferences->Mission Control->When switching to an application, switch to…”, that would be the setup you are asking for.
As for myself, I don’t use Spaces at all.
I have a keyboard shortcut for every application I use daily. CMD+CTRL plus a letter, M for Mail, T for terminal, B for browser… And so on.
Some keys are “overloaded” via Keyboard Maestro, like editor “E”: If MacVim is open, use it, otherwise open TextMate (Not using both much these days since switching to VSCode, which inherited “V” after I ditched Voodoopad :))
To make this work ergonomically, I have to be able to press CMD+CTRL with either the left or the right hand. So the first thing I do with new Macs, is remapping the right Option/Alt Key to Ctrl via Karabiner.
Using this system for the past 15 years, my worst fear is that one day Apple will close down its system so much, that this simple remap will no longer work - they are already on the hunt for kernel extensions…