For anyone who finds this by searching, I ended up staying with XFCE. Suspend and suspend-then-hibernate seem to work after following the instructions in this post. Note that you need to disable secure boot for it to work (repeatedly press F2 after rebooting to enter BIOS menu), its mentioned in the guide but I missed it the first time.
Note that in addition to adding the statements mentioned in that post to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub, I also added module_blacklist=hid_sensor_hub to it based on recommendation in the main Framework installation guide for Linux Mint in order to make the brightness up/down buttons work , so my /etc/default/grub entry looks like:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash mem_sleep_default=deep resume=UUID=[UUID for my disk] resume_offset=[physical offset for my disk] module_blacklist=hid_sensor_hub"
I have not actually monitored idle drain since doing this, will update here if it looks like it didn’t work