I too, now have lower denture and having a terrible time similar to yours.  Fixodent has a new adhesive called Fixodent Comfort.  I found it to be the best of any I've tried, including some I ordered that was made in Switzerland.  One part of success on any adhesive is making sure they are DRY when adding adhesive.  The Fixodent Comfort lasts the longest and I have actually gone through two meals before having to reapply.  Yes.....some hot soup or other hot liquids seem to reduce that time but it is definitely better than others tried.

thanks