Try to make two more changes, one of them or both of them:
1) Setting IgnoreLid=true in /etc/UPower/UPower.conf
Found here: How can I tell Ubuntu to do nothing when I close my laptop lid?
2) I had a different problem in 16.04 LTS with a laptop lid as well. I could not boot with the lid closed and was suspended.
I solved it by going to /etc/systemd/logind.conf and doing two steps:
a) Removed "#" from HandleLidSwitch, in order to activate it and
b) put "=ignore at the end
HandleLidSwitch=ignore
You will also found the second step at the same link as the first one. Hope they will help.
But, buying an alaram would not be a bad idea, because laptops is not a good idea to be turned on all day (the hours you sleep and the hours you may use it. At least buy a laptop cooling pad. They are not very expensive. And also an online UPS, but remove the laptop battery first.