If you want to try out Catalina and have enough RAM and SSD space ... I've just upgraded a Mojave VM in VirtualBox to Catalina.
The VB Guest Additions aren't supported (so no assigning host devices to the guest) but to allows you to play with the basic install and pass data back and forth using SMB/AFP file sharing with the host Mac. Annoyance of keyboard shortcuts not working or being intercepted by the VB app itself, but interesting to see what's new.
For a Mac host with Mac guest setup, I used these instructions to get the two image files from the official Mojave installer
InstallerApp2ISO - VirtualBox Utility - Download The app is built by a contributor on the VB forums.
I was trying to figure a way to keep access to a couple of 32-bit apps without rebooting. Managed to get it working but one app was EyeTV and not really usable in a VM on my Mac. I cloned the Mojave VM and then rebuilt with El Capitan (Guest Additions are supported) which worked but wasn't any better. After that I decided to play and cloned Mojave VM again and used the normal software updater to download the latest updates and upgraded itself to Cat. The only change I made was bumping the RAM to 4GB for this VM.
And half a day later there's a public beta of EyeTV 64-bit available. I should've got more sleep last night.
Now the only thing left is Office 2008. 'We' are going to give LibreOffice and O365 web apps another try since the main use is for voluntary work. The rest is non-shared home use so Open format should be enough. LO seem a bit resource heavy but should be ok for the sporadic use.
I did try getting LO to export a XLSX I created which had arrays in some functions. It didn't like them but made a usable ODS file. I then tried to get Synology Office to open it from within Drive and it refused to open it for some error. Which is a pity as I hoped to use LO on the desk and Syno Office remotely.