"We have Libreoffice and Thunderbird which are fundamentally very good, but are beginning to look a little dated."
Sadly, I found that Libreoffice is not really "very good." Libreoffice IS NOT 100% compatible with Microsoft Office - for one, It will not properly print Microsoft Excel documents, I have to use MS Office for that.
As far as Thunderbird, I still prefer to use it instead of the bloated Outlook because, as dated as Thunderbird is, in my opinion, it still has more finesse and simplicity than the Microsoft mailer. What else do I need?