I've finally got there with xubuntu 19.10 installed on my NVME disk - thanks everyone!

[Chris Green]

I have finally made it to where I want to be! :-)

I have a new, clean, install of xubuntu 19.10 which has grub installed
on /dev/sda and /boot on /dev/sda1 (sda being a SATA disk which the
BIOS can see) and the rest of the installation in my new NVME disk.

I have also still got my 'old' xubuntu 19.04 (on /dev/sdb) and have
got it added to the grub configuration that the 19.10 installation put
on /dev/sda.

So I can now, in stages, add the required bits and pieces to my new
19.10 installation but go back to running 19.04 when needed.

Thanks for all the help and explanations everyone, much appreciated.

-- 
Chris Green