I am quite happy with The Great Suspender for automatically suspending tabs - has a good range of options for tweaking.
https://chrome.google.com/webstore/detail/the-great-suspende...
https://chrome.google.com/webstore/detail/the-great-suspende...
https://chrome.google.com/webstore/detail/onetab/chphlpgkkbo...
edit to add link: https://chrome.google.com/webstore/detail/session-buddy/edac...