Which camera would be good upgrade from *ist DS

I'm looking to upgrade my equipment next year and need some suggestions.
I currently am using a Pentax *ist DS and want to stay in the Pentax line. My interests are capturing butterflies and other wildlife and also would like to be able to get good shots of my kids (portait type shots).
I don't want to spend big money on the upgrade. Would the K-7 be a good choice or would one of the other cameras in the Pentax line be better?
Thanks for any advice that you may throw my way.

I upgraded from the *istDS to the K-7 last year, none of the other models had the top LCD which I use all the time. I also wanted video so I felt going to any other model than the K-7 would have been a downgrade.
The *istDS kit was a AUD$1400 purchase back in 2004, so spending what I did on the K-7 felt quite reasonable.
Ironically, although I love the ergonomic of the K-7, I still feel more comfortable with the *istDS.

Any current Pentax camera really..... just depends on how
much you want to spend.

And how it feels in your hand

If you like the size of the Ds then you need a smaller camera - definitely not a secondhand K-20D. I moved from a Ds to a K20D and found it heavy and brick like.
The K-5/K7 is smaller and nicer to hold. The K-5 is closer in feel to the Ds but like Sledger I too secretly prefer the feel of the Ds .

If you don't use the top screen, and don't mind a Pentamirror instead of a prism then a K-r, or a K-x may feel better - they are lighter certainly. There are other restrictions with those two (no weatherproofing for instance) but they are certainly worth considering.

But really any of the current range would be a good next camera. How it feels in the hand is important, as well as how much you want to pay. You can't really go wrong with any of them tbh.

I've just upgraded from ist Ds to a K-r. All going well so far. It feels very similar in hold and weight. I'm getting used to the differences slowly but its quite a jump spec wise!

Thanks for the comments