I can totally see how you use knitting in therapy or for reasons of self-therapy.
A friend of mine who was stationary in a place for sime time was adviced to knit. So: yup, ggod idea.
I like knitting for others but I also like knitting for myself. Maybe you need to make something for yourself? But if it shall be for your grandson that gives some extra satisfaction when given away.
A blanket... well, how about you buy a few tones of blue, that you like. Nice, soft, easy and blue to your heart's content. I am thinking of 3 tones, maybe another one in a color changing yarn? Just keep them all the same style / type for mixability.
Talk to your LYS about the amount you need for a blanket (for example for a 3 by 3 foot or something smaller...)
And then you knit squares. maybe make the blanket 4 or 5 squares wide, maybe more. You will know how big a blanket you will want - so you do the math how big to make the squares.
Make most of them garter stitch (just knits on both sides) so they are easy and quick. Make a few stochinette stitch to challenge yourself. Maybe make a few that have stripes in the different colors. Or ribs of garter next to stochinette.
Make one that is ribbed ( a few stitches bigger than the plain ones, because ribbing pulls in) and make one in seed stitch or moss stitch, if you like?
The colors you just use to your own satisfaction.
In the end, sew them together to a wonderful blanket that shows all the different colors. That project is not as scary as a whole blanket, but once you achive the goal, you are done. Really done!
The colors you can use by mood. The texture and therefore difficulty you can do by status....
If you ever come to a mood that requires green or red... well, you can always go to bright and colorful, you know? But all blue would be very nice, really.
since you may not always have the intent to go through one piece and then the next: organize several sets of needles in the same size and keep different parts of the project on them at the same time. And if you want to switch: then do. They will all come out at SOME point.
If you want to make a border later on: well, fine, if not... just don't. The kid will not complain and it is just another style anyways.
Let me express my hope for you that you get yourself together again. Take all the help you can get.