I looked for something like this several months ago (before Apple announce the feature would be in iOS 13). All I could find was the original Swype keyboard, which I’d downloaded years before. It’s no longer available for download by new customers, and the competitors all require full keyboard access, by my research.
What don’t you like about the stock keyboard that makes you want to use a third party keyboard instead?
MessagEase.
When I switched to it I felt so liberated from the tyranny of autocorrect mistakes.
You can turn of auto correct and all the gimmicks like spell checking, predictive typing, smart punctuation and auto capitalisation for the stock keyboard by going to Settings > General > Keyboards
Yes, but a QWERTY touchscreen keyboard needs some smarts to be usable. MessagEase doesn't.