Lubuntu 14.04 wants to upgrade to 16.04. Any solid lightweight Ubuntu?

Hi guys! So I installed this system to purpose mainly as server, but from time to time I’d like to have the desktop environment available to handle things within a graphic environment. Usages are mainly Seafile Server, Crashplan Backup and OpenVPN. All the storage to seafile and crashplan are handled via NFS mounts to a NAS, has been working very reliably for nearly a year. I’d also like to consider remote desktop (x2go if the possiblity exists).

Up until now I’ve been more or less happy, even though I believe the kernel is starting to be outdated. But now it started prompting me to do a release upgrade. Luckily I made a whole SD backup, because it went as bad as you can imagine. So after restoring, I’d still like a more recent Ubuntu system. One of the reasons is I believe with more recent libraries I might be able to use an alternative X2go agent which might work on ARM. I’d like it with a lightweight desktop (XFCE, LXDE) which I could bring up or kill at will from the console if possible…Could you guys point me for a reliable option where I can expect it to keep up to date?

Thanks a lot!