First thing you need to do is to make sure the "smart outlets" are capable of handling the maximum voltage and amperage of your heater. You don't want some attempt at making it smart to result in a fire.
Most oil filled radiators have a thermostat on them. Use it and with some tweaking it should work fine without getting alexa involved.
K.I.S.S.
This is how ALL door handles with locks are required to work now.
At some point building codes made it so residential door handles must open from the inside. This is to ensure if you are trying to get out you don't have to find a key or fumble for the lock during a stressful and dangerous situation.
You could add a deadbolt and use that to keep the door closed. Or add a hotel lock or something similar higher up and out of your kid's reach.
You could also set it up so when the door is opened you get a notification on your devices. Set up an announcement across any speakers.
Don't use a surge protector to connect to the UPS.
Get some smart plugs, a couple power strips (not surge protectors), and an UPS.
Plug smart plug into the power strip and power strip into the UPS.
Solved.
End User Windows has a shit history with forcing updates on you and reboots just because you waited to long.
End User Windows is also not great at managing large numbers of storage drives.
They also aren't great to manage remotely.
What you seek doesn't exist.
There are some options that come close but require tinkering and adaptation to work in HomeKit.
I know I missed some and may have some of the information here a bit wrong. But what you seek doesn't exist which is why you can't find it.
Too many people are trying to overcomplicate things.
I used oil filled radiators for years and never felt the need to make one smart.
Heck a ton now have clocks with multiple on and off options on them. So you can schedule it to turn on and off so you don't need to touch it.