How do I translate "舒服不如倒着，好吃不过饺子" in English?
As with most idioms, there's a couple ways to translate this non-literally. 

If you want to go the old fashioned route, you can maybe quote from the Bible like:


  There is nothing better for a man, than that he should eat and drink, and that he should make his soul enjoy good in his labour. (Ecclesiastes 2:24)


Or maybe the Spanish idiom:


  A full stomach makes a happy heart. (barriga llena, corazón contento)


You could of course modify those to be about dumpling specifically: i.e. A stomach full of dumplings makes a happy heart.

Or you can just try something from yourself:


  Life doesn't get better than relaxing in bed and eating delicious dumplings.