I'm poor, so I use a variety of free tools to make things happen.
When I'm writing my rough draft I go WordCounter.net. As the name implies, I use that to see how many words I've written since webnovel readers expect an average of 1,500 - 2,000 words per chapter. I also like some of the stats I'm given such as the reading level. It also automatically saves your progress, no matter how many times you leave. The next time I go to that site, my progress is still there.
But still, things can happen, so I transfer my progress to Notepad. Regular ol' notepad since all I'm saving is plain text. Any formatting of the text will be done later.
For spelling and grammar, I use Grammarly, which you find to be cumbersome, and maybe I do too. That's why I have that installed in Chrome, but I use Firefox predominantly. I go to the previous mentioned WordCounter.net and just use Firefox's spellcheck... to retype the word until I get it right. Spellcheck on Firefox is pretty jank if you ask me. When I finish my draft, I then open up Chrome and go to MemoNotepad.com. That is where I use Grammarly for their suggestions, and only that, suggestions. Even Grammarly has its issues. After I'm done, I save it back to Notepad.
I then go to Google Docs and do the same thing, just use that as another way of getting suggestions since Google uses it's own grammar system... I think. I'm not sure but I figured I might as well use it.
But after all that, it stays in my Notepad. It's in my hard drive, I can transfer it easily through USB stick or uploading it on Google Drive. It's a relatively small file that it would take trillions upon trillions of them to fill up a gigabyte so I don't even worry about how much I have. I can even search for specific things by the folder's search option and find what I need.
Maybe this method may not be with you, especially since I use my laptop to write, only because I have no other choice. You also seem intent on using an app, so I figure you want some features built in, where as my method gives you no such luxury. Still, I figured it may give you an idea to consider using it, but again, I do this because I'm poor, been poor for so long, and got so used to it I might as well stick with it.
EDIT:
Actually, I just remembered, I wanted to use this:
Novel-writing software designed and coded by an author, not a salesman.
www.spacejock.com
It's a program designed to write stories as it organizes stuff, but I found it too convoluted. Still, maybe you can give it a shot. Though I don't think it has spelling and grammar check. It's purely for writing and organizing.