I would consider anything that contributes to your good health and happiness and anything that helps you perform on your job a need. Sure, things like glasses and a mattress or clothes that don't have holes in them might not be as important as say, food or water, but they should still be considered a priority.

I would recommend finding a way to either bury or eliminate your guilt as it's going to do nothing more than hold you back from happiness and health.

Finally, if you're struggling financially, than getting a job that pays well and isn't hard on your health should be a priority. Take care of you first.

You're important and you deserve to meet your needs. Don't let anybody or anything convince you otherwise.