When decreasing stitches on a circular needle what do I do when less stitches make it too tight to continue?
This is when (dpn) double pointed needles come in handy. When the stitches are to tight then it's time to transfer those stitches to 3 or 4 double point needles of the same size. (some dpn come in set of 4 needles and some with set of 5).
You can also use two sets of circular needles to decrease also. Make sure to knit stitches off the same needle that holds the stitches otherwise you'll end up with needle pointing the wrong way.
I made a video on decreasing a crown of a hat once. I think it might be helpful to see it. Here is a link to the video;