Fontanel as Hydration Indicator?

I've read or heard in various places that a sunken fontanel signifies
de-hydration. Of course my husband and I lightly touch our darling son's
fonatnel throughout the day and of course it feels slightly recessed at times
and level with the rest of the skull plates at others.

Over the last four days I have taken a huge leap of faith (with your
encouragement and support) and thrown away the formula I was using as a
supplement. I've been night nursing with great success and it seems like I have
way more milk as a result especially based on what I've gotten from pumping
(much faster yield, much more). I feel very proud of myself that I've made it
to today, six weeks, and I really want to go on as long as I can.

Question: our son has many wet diapers and seems content (although he's crying
for food less than usual- maybe because he's getting older, maybe because he's
nursing longer at our night nursings..not sure what do you think?). I nurse him
on cue and sometimes he stays at the breast for ten minutes sometimes for a
half hour. However, it is very tempting to offer him a bottle of formula
especially when he's nursed for so short a period and seems too sleepy or lazy
to go on or when we see that fontanel that seems sunken to our paranoid
first-child parents' eyes

Please encourage/advise. You have all been so helpful and are the reason I've
made it this far

Thanks,
Lisa