YourITronics has a good article on making a Constant Current Source using a Texas Instruments TPS54232 chip.The TSP 54232 is a flexible little chip but you will need to get out the fine pitch soldering iron tip and cut down on the coffee since it is only available in a surface mount package. There is an interesting DIY thermal via system that is used on the board to allow the non-etched copper of the back of the board to be used as a heat sink.
“The solder drops that you can see on the back of the board are a sort of DIY thermal vias. I’m not sure how efficient they are but I gave them a try with this board, probably because I had too much time available. First when I designed the board I included a area of copper in the top layer right beside the resistors. Next I drilled some 0.7 mm holes and I placed 0.7 copper wire in the holes securing it by soldering on both sides. The trick is to make the solder joint as small as possible so it doesn’t spaces your component from the board. As I’ve said I don’t know their efficiency but I think they work, I can feel the heat transferring from one side to the other faster. If you like them you can try them.”