You cannot upgrade as it is too big a step; so you should really back up /home and any mysql databases and do a fresh install of 11.2 as 10.3 is no longer supported.
IMHO you should wait at least one, and maybe two more months, until many of the bugs are ironed out of 11.2. And then update to 11.2. As you noted, 10.3 won’t get any more security fixes.
When it comes to do an update, I would do a clean install. I would back up everything to an external hard drive, and then CHECK to ensure the backup is good (as many users mess up this backup), and then do a clean install of the / and also a brand new formatted /home. Be especially careful with your emails, email addresses and book marks. Maybe make 2 backups of your emails and email addresses.
11.2 uses ext4 and this is a good opportunity to move both / and /home to ext4. Plus clean out your /home.
Also keep a backup of your /etc and /boot, so that you can review the config files there, if you have a problem configuring 11.2.