Hi all
So I did a bit of reading from 'Heir to the Empire' which is the first book to mention the Ysalamiri and discovered the following which might or might not help.
They are no more than 50cm long and not predatory.
Their claws grow directly into the branch they are living on, which indicates they feed from the sap of the tree for most of their life not moving around.
They are described and quote "Fur scaled salamander like creature."
And at one point it's referred to Thrawn stroking its long neck.
I found this picture which fits in more with their description (although I get the impression its neck could be longer,) as the pictures posted so far seem more lizard and predatory looking, and they defiantly don't do the whole neck scarf thing.
As for the frame it's described as thick and heavy tube, and wraps around the neck and back, and at one point is called a nutrient frame.
That can be interpreted any number of ways, but if I were making one I would go for a backpack type frame that starts at the bottom of your back and just comes over the top of the shoulders, and the Ysalamiri would be still on its branch but fixed to a frame. Being a costume item, used at conventions and such like I always feel the public like things to look at that work, so as they refer to it as a nutrient frame, I would incorporate a couple of small sealed canisters of coloured water and a small 12v pump to pump it around some clear tube wrapped around the frame and feeding in and out of the branch the Ysalamiri is on, and something sci fi mechanic like on the lower portion of the frame which would power it all. As its referred to Thrawn reaching up and stroking its neck I would mount one across the shoulders leaving the lower frame to mount the other stuff to.
I included a very rough sketch if I were making it, using copper tube for the main frame as it's easy to bend and work with, and still light then attach a real or plastic log drilled to take the clear pipe, then construct something to go at the bottom of the frame tech wise looking like other star wars stuff does.
You could then get off ebay or local hiking shop some backpack padding for the lower back and shoulders and have shoulder and waist straps to hold it on. However that's just me and my interpretation of what I would do.
Don
Ps, forgive my stick Ysalamiri I'm not good at drawing creatures