I wrote a pretty nifty jQuery plugin that mimics the Tumblr default except it adds even more cool features! https://github.com/PixelUnion/Extended-Tumblr-Photoset
If you run into any problems using it, don’t hesitate to post an issue on the repo.
One thing that will work perfect for you is that it’s entirely flexible and will fill the space of whatever container it is in. This means you won’t need to worry about loading in a different photoset, it’ll just expand/contract accordingly.