I don’t understand why you are completely focussed on messaging? How do you actually sell the products, do you have an online shop?

>Running a ‘Conversions’ campaign with three different split tests, optimised for ‘Impressions’, ‘Link Clicks’ and ‘Daily Unique Reach’ – no success

None of these things will work. You need to optimize for the action you actually want people to perform or performance will be terrible.