You can use Firefox bookmarks to do this. Select as many tabs as you want, right click, and you can create a bookmark folder containing all your tabs. When you want to reopen them, right click on the bookmark folder, then click “Open All Bookmarks” if you want to open all of them at once.
Why do you want a VPN? Is it just for some light piracy? Staying safe on public wifi? Or do you actually NEED to maintain your privacy, with real consequences if you can’t?
If you need true privacy, the answer is Mullvad. But there’s also more required than just switching on a VPN if you want privacy. If you want a convenient and easy VPN that’s part of a bigger privacy-focused suite of tools, then I’d recommend Proton. They make some pretty good products.