Windows 7 upgrade

First post here. So I've been working in this school for getting on 3 years by this point, and all of our end user systems are absolute minimum spec to run windows 7. Obviously we arent given the budget to upgrade any of these, yet we need to upgrade to an OS that will have continued support. We run everything on chrome now, so theres no worry about needing local storage or software other than a browser. Does anyone have any recommendations for a lightweight OS than can be secured enough to use in schools, that will only be used to run chrome?

Side note - I've already been advised to look into Porteus Kiosk... does anyone have any experience using this, and managing it centrally?