The backpack doesn't have a waist belt, but the shape of the back section makes it quite well adapted. 

The large variant is supplied. 

K&F Concept sling backpack you are asking, our backpack size is L x W x H:23×14×37CM, and your Nikon P1000 size is 15*12*18cm, can be used on our backpack, please have a try. if you need more information please let us know. 

Size Name: 9.06"*5.51"*14.57" sling camera backpack you are asking, we checked your Canon eos 600D size is 13*10*8cm, and 55-200mm lens size is 7*10cm, in our bag, the bottoms size is 22*18cm, when put your lens+camera, lens length 10+camera height 8=18cm, which is smaller than 22cm, so please trust to purchase, fit for your needs. if you need more help, please contact us.