How to stop iOS from autocorrecting actual words??

I've seen variants of this question asked and some are very old, for much older versions of iOS. So, now in iOS 12, how do I get autocorrect to STOP changing ACTUAL English words to another word? This isn't something I can handle on a word-by-word basis by maintaining a huge dictionary because they're real words. And I don't want to turn autocorrect off completely. If I type "gello", I want it to change it to "hello" because "gello" isn't a word and the G is next to the H. But, if I type "them", I DO NOT want it to change it to "then". It'll even do it when the context of using "them" was correct but "then" was NOT in a correct context. What the heck did Apple do to mess this up so badly? This is a deal breaker for me so my next phone will be an Android unless I can fix this behavior.