Congratulations! Your new family member will bring you years of joy and happiness I'm sure. And if your Yorkie mix is anything like my Yorkie, she'll keep you smiling too! They are too smart for their own good, and can often out think us mere humans.
As for your questions around gates...I personally have not ever used a gate...I crate trained both my dogs...however, I did do a quick search for you and found this site that might have a solution that works.
Pet Gates, FAST SHIPPING Wide Dog Gates, Tall Dog Gates, Free Standing Pet Gate
Others with more experience might have better advice. Best of luck...and Welcome to YT.