Do you have a Sam's Club? I actually use my shipping scale that I bought there for about $40. They have to sit on it (it's about 12" square) but even Loki can sit still on it long enough for it to be accurate. It's *extremely* accurate. I usually weight boxes between .5 and 5lbs and the ladies at the Post Office always comment on how perfect my weights are. That might work? You can "tare" it so if you want to put something soft on top for them to sit on you can do that and it's still accurate.
This is the one I have:
Amazon.com: Royal EX-315W 315-lbs. Commercial...