Decided I wanted to work VS Decided to work

The subject of decided is I. I decided I wanted to work, is the more formal sentence.

The differences in Decided to work or Decided I wanted to work only has to do with why you decided to work. Perhaps you needed the money despite not wanting to work. You may decide to work having nothing to do with wanting to.

"Wanting to work" and "working" are not the same thing. You can want to work but not be able to, meaning that you want to work but don't work. You can also work for other reasons than because you want to - because you've been forced to or because you need the money, or because it might lead to something you do want. Then you work but don't want to.

Someone who decides they want to work abroad might still not do so. Someone who decides to work abroad might not want to.

"Deciding" is also night me same as wanting. Deciding is to choose between two options but the will is not always involved, Someone might decide that the answer to an exam question was A rather than B, but the will is not involved.