This is 60 litre - there's 90 litre as well.
Bit hard to move around if theres not standing room.
I would say forming a perfect seal is not an issue if you put anything that you want kept clean into a plastic bag. I have found the main problem is that anything in boxes with stuff stacked on top tends to get lost or forgotten, since you tend to avoid the effort of restacking everything. I like the shelving idea better.
... except the OP specifically asked "Where can I get decent 60l type boxes with a seal?"