Simply Indispensable review for Buy Button channel

I only require the Buy Button as I am a very small business and already have my website hosted externally to Shopify so cannot justify the cost of a Shopify hosted store (x 3 times the cost of the Buy Button). The one thing I have found so far that is very frustrating is the inability for customers to leave a note via the Buy Button for delivery instructions etc - Cart Notes. I have reached out to Shopify Experts twice however they really only seem interested in setting up stores etc. I am not in need of this service. All I need is Cart Note integration. Regards