Looking for a butt plug that is similar to the Tristan that has a bit more staying in place power.

There are two great toys made of metal and silicone that are shaped very much like this, this shape is excellent for remaining in because the handle is tapered to rest between the cheeks naturally. link
So, depending on your material preferences, either that one or this: link

I think Veteran makes some good suggestions there, but I was wondering if the problem with staying in place has to do with the base or if it is the head/neck difference. If it is just the base, then you might consider trimming some of the material off the base of the Tristan so that it is able to rest more naturally. I tend to favor plugs with flat bases for extended wear because I feel like the handle ones aren't as comfortable if I choose to sit down. If the problem is really head/neck difference, you might consider the Ryder link (which I really love), and the Joe Rock link

Jimbo is right- the staying power of a butt plug has to do with the difference between head and neck size, though the base does contribute to wearing comfort. I second the suggestion of the Ryder.