It's my believe that you being their child was good enough. As you say they pampered you so being you is what you did for them. That is enough and you could not have not done more to help them with.
Sometimes we do something back in deeds or with money and at other times it is by just being around. Don't let the idea you could not do anything back eat you it is nonsense and not important. In the end all a loving parent wants is that a child feels satisfied, loved and at times happy. So if you want to do something back try that, even though some days will be sad.
Some sadness,this sadness due to the loss of beloved ones remains but if you could not feel it this means you never loved, appreciated and missed them.

If there is no one around to pamper you be good for yourself and reward yourself, hug yourself and look in the mirror so you can see your parents.

A warm embrace to you.
🍀♥️