@kev first step would probably be to convert your current notes and todo list to an ‘open’ and ‘portable’ data format. I prefer #asciidoc but #markdown is the easier choice.
Search the web for ‘github onenote2markdown’ and use a tool you feel comfortable with (read the issues etc) to get everything converted. Then any editor that has a Preview feature for your chosen open format would be enough.
No more vendor lock-in, no more proprietary formats. Be free!