If you want it to be rock solid, put it in writing in a living will is other people have said. But it doesn't have to be this formal. If there are no formal instructions, the healthcare team will ask your family what to do. If you've been clear with your family (and have a good relationship with them) they will be able to relay your wishes to the health care team.

Blood is also a laxative so it tends to travel through the intestines quite quickly reducing the opportunity for absorption.

I mean, wealthy people are doing this all over the world as we speak...

Warm is relative term. If it's 10° below zero and -30 with the wind chill, you will automatically feel 20° warmer in an igloo since it blocks the wind. Then it will also trap body heat which could get it up to 25 or 30°. At that point the feels like temperature could be 60° warmer than outside, but still be below freezing. Also, the blocks of an igloo are quite thick, so even if the air inside is a bit above freezing, it won't completely melt the igloo. The inside layer of snow and ice might start to warm up a bit, but it will also constantly be cooled by the rest of the ice block.

There's a bar in my hometown that does this, and the sign above the urinal says something like "Don't worry, we only use this ice as a last resort"