Thank you for your insights. I will try that next vacation.

Magnesium Chloride is the cheapest, magnesium oxide has the strongest laxative effect. Take between 5-10 grams per day spread out throughout the day. That will yield around 625-1250 mg elemental magnesium, 1.5 to 3x the RDA, but you likely need to it up from a deficiency. There is no way to overdose (gut rejects it automatically).

I have been told that oxide is not very bioavailable at all, Magnesium Citrate or Glycinate are better.

magnesium oxide ok? (cheapest one)

Get on a lot of magnesium + thiamine (this is important, they go together). Whether you quit coffee or not, but these two will help you with the withdrawal symptoms (and they are BOTH depleted by regular caffeine intake).