I'd really like to turn off the feature that tries to correct some previous word based on the next word. Most often, that mangles the last word because I swyped the next word wrong, or I just really wanted to type something different.

There are several levels to the autocorrection, so you can definitely do this. I've turned most autocorrect off on my iPhone at this point, because the people I talk to on a regular basis have a much easier time figuring out what I meant from regular misspellings than from the complete rewrite of phrases that iOS is fond of doing.