you've probably seen all this before, but here's what (i think) helped me raise my blood pressure a bit (still low/normal) & got rid of my postural hypotension.
- reduced my Magnesium supplement intake from 600mg to 400mg (elemental magnesium). I read that Magnesium lowers blood pressure.
- supplemented with salt tablets (600mg sodium chloride per tablet); i supplemented for about 5 days, starting with 1 tablet & built up to 3 or 4 per day.
- reduced my water intake until there was colour in my urine. i was over-hydrating & most likely throwing all my electrolytes out of balance. i was peeing a lot (too much, too often) and it was usually clear.
That seemed to work for me.
Since then, i replaced the salt tablets with fine sea salt (white, not coloured, 100% sea salt, no flow agent etc) & may be take 1 salt tablet after a sweaty workout.
I also added potassium chloride powder to the mix, because i think my diet may have been deficient when compared with sodium. probably dose about 1/4 tsp KCl for every 1/3 tsp sea salt one to three times per day depending on 'gut feel' (am i craving salty foods) & sweat loss.
& also still making sure i have colour in my urine, which is harder than it sounds for me, i find i can easily over-hydrate & have clear pee.
For me, it seemed to be all about electrolyte balance, & i focussed on sodium, potassium and magnesium.
It may be worth checking your daily electrolyte intake using something like cronometer.com (if you haven't already).
Side Note, my body temps are on the low side, unlike yours.
Edit to add a bit more info (follow up to comment);
I should add that other things that i discounted that may have similar symptoms to postural hypotension were anemia (via a blood test) & hypoglycemia (low blood sugar), i have my own blood glucose meter. I also bought myself a blood pressure monitor to monitor that.
Magnesium did seem to help me a lot with various complaints, in my particular case i believe i was deficient at one time. I was probably supplementing with up to 900mg per day at one point. But then i stopped feeling any 'improvements' & started reducing the Mg.
I now take 200mg elem Magnesium (in the form of 1.3 grams Magnesium Malate) twice a day (one in am, one early evening).
I think getting the balance right is the key; magnesium/sodium/potassium.
Magnesium lowers blood pressure (google for refs), so i may have gone overboard (esp in ratio to sodium & potassium).
& drinking excessive water (more than the body needs) can dilute your body salts (electrolytes).
The 'drink 8 glasses of water a day' thing is a myth. water requirement (& electrolytes) will vary, that's why i generally go by 'feel' & urination frequency & colour.
remember you will also be getting water from food (esp fruit & veg) & liquids (tea, coffee, milk, juices..etc).