Any recommendations for a travel mug that would work for using with frozen smoothies? Must have a really good seal so it can reliably go in a bag and not be at risk of leaking. I'm struggling to decide what might work with the thicker liquid as traditionally you would look for a straw but a straw would be a bit of a pain for bag storage. Would also love it to keep it cold until lunchtime so say 5 hours from making. Any suggestions?