I take 300mg Magasorb Ultra (magnesium citrate) from Natures Best, who produce good quality and reasonably priced supplements. They're cheaper, and often higher potency, than Holland and Barrett. Most people are deficient in magnesium, and it's involved in so many bodily processes that it's one of the best supplements to take. It's good for mental health generally, and since I increased the dose from 150-300mg I feel less anxious, my mood has improved, and I'm sleeping better. It can have a slightly laxative effect, so it's best to start on 150mg and see how you get on with it. I haven't have any problems since upping the dose. They also sell it as a powder if you struggle with large tablets, but that works out more expensive. You can take up to 400mg a day. If you decide to try it, don't buy a cheap magnesium oxide product as that's very poorly absorbed.
You can also use magnesium oil spray, which is well absorbed, and you can make it at home for pennies (google for the recipe) rather than buying expensive sprays. Epsom salts baths are another good way of absorbing magnesium through the skin, good to do a while before going to bed to aid relaxation and sleep.
L-theanine is good for anxiety, also available from Nature's Best. They also make one with lemon balm added, which a friend finds very helpful. If you contact their nutrition advisors you can request a sample, but they'll give you a full refund if you buy a product and find it unsuitable. You can also ask them to suggest which supplements they recommend, as there are others that can help with anxiety, including ashwagandha.
I hope you find something that helps, anxiety is awful. Guided meditation is very good for relaxation, there are some great ones on YouTube. I found a lovely one with gentle ocean waves, I think it was made by The Honest Guys.
