I currently take 3.5 mg of boron but I think most ppl say 3 mg is fine. https://www.betterbones.com/bone-nutrition/boron-for-bone-health/
I was taking 3 mg of boron daily but recently started taking Jarrow’s BoneUp as one of my calcium supplements. 1 serving of BoneUp is 2 pills and contains 1 mg of Boron. I only take 1/2 serving or 1 pill, that’s were I get the extra 1/2 mg of boron from.

For magnesium, I’ve read that if you take calcium supplements you should supplement your magnesium by 50% of the amount of calcium you take. Ex. if you take 500 mg of calcium via supplements you should take 250 mg of magnesium. If you take any medications, you need to make sure it’s safe to take magnesium, just ask your pharmacist. Too much magnesium can cause nausea/diarrhea, which is actually a pretty easy way to find out if you are over doing it. I’m currently taking approximately 183 mg of magnesium daily. Again, the odd number is because of the Jarrow’s BoneUp. I had been taken 200 mg of magnesium citrate, but the BoneUp contains 83.35 mg of magnesium per pill, so when I started taking the BoneUp, I reduced the magnesium citrate to 100 mg.
https://pubmed.ncbi.nlm.nih.gov/33959846/
I recommend doing a little research before adding magnesium to figure out what form would be best for you.
https://www.healthline.com/nutrition/magnesium-dosage#types