Hi,
I am a Dutch product designer, based in Hong Kong and work regularly with London start ups. I have worked on many different products, all plastics (headphones, babaystrollers, Senseo coffeemachine for Philips, etc). However.. what do you actually want to design, the plastic or a plastic holder for the cup!?
If it is packaging design, you need a graphic designer, I cannot help you with that.
If it is a plastic product, I can help you. As well regarding sustainability, etc.
Feel free to post me a message for further explanation of your request,
BR, Bauke