Emacs already has you covered. Good old C-x RET C-\ TeX will switch your input method to TeX, converting \alpha etc to unicode alpha, etc for most math symbols. Additionally, ^[char] or _[char] will become superscript/subscript unicode chars.
Once you've done that once in the session, you can just hit C-\ to toggle it on and off (C-x RET C-\ [input method] actually lets you select from a wide variety of input methods, and C-\ toggles on and off the most recently selected input method).
Once you've done that once in the session, you can just hit C-\ to toggle it on and off (C-x RET C-\ [input method] actually lets you select from a wide variety of input methods, and C-\ toggles on and off the most recently selected input method).