Triboron is an option if you feel the borax is unsafe to take. Or one kilo of apples with core a day; then at least you have the RDA of it:)
A very few people have had a strong reaction to boron (all on CZ no one in real life, my experience) It could be a highlighting of a problem, same as Iodine even very small amounts may create. But I dont know the outcome. Probably other issues than the boron, if to follow my hunch about it.