I can relate - we too had to create ways for our older dogs to be able to get away from the teenagers/puppy punks ... Just be careful that the cat tree is not high enough to jump/fall from ... Maybe some pillows underneath for safety? I fostered and rescued many little dogs and all of them are at risk of serious injuries even just jumping from a couch. My vet recommended not letting the little ones do stairs even ... as the constant impact is hard on their joints - we installed ramps. However ... I too have a mountain climber yorkie mix here and at 12 weeks she loves to climb trees, the couch - any and all high ground ... her brother can climb wire pens and gates like some free climber ...
... it is a constant struggle to keep these nutters safe - small but mighty hahaha ...