Amp Slide Cart Upsell Drawer

I initially tried 'Up Cart' as this appeared to be the market leader. As it turned out, their customer support was extremely disappointing: specifically, the actual web dev guys were simply not helpful enough and were trying to avoid dealing with my requests. Slide Cart however were committed to making sure I had everything just how I wanted it, and it functions perfectly. Whilst it's not at all cheap, it's about who can best solve the problem. Highly recommend.