I am so sorry for your loss of Cuddles. I know that you and Nibbles are missing him a lot.
As for getting Nibbles a new companion...I have a couple questions. How tame is Nibbles? Does he really enjoy human company and being handled? If so, you could consider becoming his "surrogate" companion. If you would have an extra 30 minutes or 1 hour daily to spend with him, in addition to whatever time you spend now, he could adapt quite easily to life with you.
However, if he isn't super tame, and doesn't enjoy being handled, or you just don't have the extra time to spend with him, getting him a new companion might be a good idea. It would be best to get a younger Goo, so that Nibbles might feel a little "fatherly" towards him, rather than seeing him as competition. It's not really easy to introduce new Degus, but if you're patient and take your time, and they like each other, it might work out well. Worst case scenario, if they can't get along, you could just keep them in separate cages right next to each other.
Check out Amethystbelle's webpage dedicated to Degus. It has a good section on introducing new Degus, and might give you some ideas:
http://www.degurock.moonfruit.com/
Again, I am sorry for your loss. Losing a Degu is really hard, they are such special animals.