Great question and as a writer I am there with you. I know that if you are writing things like novels you will probably never catch every single mistake but here are some tips I've found to help with that.
The first is to use Grammarly. There's a paid version but I use the free version and find that it really makes a huge difference. It can be added to MS Word and Google Docs (which are what I use for writing) for free and makes suggestions based on the context of the sentence. Its not always right but I find it works better than MS Word's spell checker. Link below.
https://app.grammarly.com/
The second tip is something you've already alluded to. When you edit your work, change the font. The reason you catch more when you go from hand written to typed is because your brain isn't glossing over the words as much since the fonts are different. Each time you edit, change the font to another (readable) font. Once you're happy with your editing you can swap it to whatever font you want it to be in.
The third tip I have is something I learned recently. Have a program read your writing to you. I use MS Word's reader for it. Since your brain skips words that look close enough to be spelled correctly, some spelling errors can be hard to catch. The voice reader speaks literally so its easier to detect a typo or if a sentence doesn't sound right. Also its hilarious to listen to.
Regarding your experience using a smaller window and Notepad so the screen isn't as distracting, I don't see why you can't use those as part of your editing process. I don't have that issue but I also have lots of practice reading through large pieces of coding when I'm programming so a block of text doesn't overwhelm me anymore. Depending on what you're writing you may go through several drafts using each technique once which will most likely give you the best chances at catching the most amount of typos. :)