Hi Folks

I have recently bought my first garter snake, shes a female checkered and I have her in a 4'x2'x2'. My intention is to add one or two more other speciies of female garter. I was hoping to get a black necked as I really like the look of them. Is it ok to add a black necked and what other species could I add?
Where can I get them in the UK?

The one I have I bought as an adult and it looks like she hasn't been handled much, she musks and bites quite a bit. Will she get better with handling or will she always be like this now that shes an adult?

Thanks

Stan