Akin to placing the bag or your pad on a sheet of ice.

Cot is better because you add an air insulation (even cold air) between you and the heat sink of the earth. What you have to watch out for is a wind/breeze blowing under your cot, but that can be managed. Stay off the ground!

The way to do it is this: cot off the ground, gear under the cot. Sheeting is optional.

Quality mat with r value on the Cot. Blanket on the mat.

Sleeping back, preferably Wiggy’s hunter antartic on the blanket.

Liner in the sleeping bag or blanket.

You between the liner.

Blanket on top.

Key: ALL NEW CLOTHES at night, yes even your undies and especially socks. Your own sweat is your worst enemy. Bonus for two pairs of socks with feet warmers between.

Thermal underclothing works.

A buddy heater will warm the tent to allow you to change comfortably, turn the buddy heater off at night, the above method will keep you warm so no need to risk fire or carbon monoxide gassing while you sleep. Buddy heaters are a wet heat anyway, so you really don’t want extra moisture if you can help it.

You can cheat and run a diesel heater (combustion is outside the tent and heat is dry), but that shouldn’t be your primary system.

But yes, a cot is superior, IMO, and my go to for the past few winter camps, last time I was on the ground was scouts and it sucks, especially with cheap gear.

I didn’t even have my bag zipped up all the way this past camp, but it was a mild December low was probably 20F.

I was warmer last December than on an air mattress on the ground, same sleeping bag, which is my system when spring camping.

Bottom line is you aren’t going to sleep well without quality gear. It’s not cheap.