Advice needed on supplements

Can anyone give information on the supplements to take to prevent OP from getting worse, and the 'brands', they use. I was taking Osteo Support from the Natural Health Practice, but they are very expensive. (£48 for 60) And my GP told me to go to Holland and Barratt.

But all the supplements they sold were with 'carbonate' not citrate. 'Carbonate' is the 'cheap' form of the supplement.

I currently have Vit D which I buy from the US as it's in an oil gel, Cod liver Oil capsules.

Any info about what other people take would be much appreciated.

Thank you
Sarah