Running Win10 and I edit a lot of photographs and PS7 does what I need it to - auto contrast/levels hotkeys, precise picture rotation (not just 90 degrees), etc. Tried Paint.Net and hated it... but there has to be something more modern (but free).
If by 'a lot' you mean this is not a hobby, but more of a semi-pro or professional thing, then anything 'free' is going to be a whole lot less able than PS7 is currently. It'd be like using MS Word 13 and comparing it to Win10 Notepad.
If it's really that important, bite the bullet and upgrade to CC, you'll have the same structure you are used to, with all the extras added on over the years.
Just saying it sounds more like a 'want' than a 'need' as PS7 seems to be just fine other than old.