ellemea,
Unfortunately lower dentures will always be a problem. You will never get them to be perfectly snug unless you have a few implants placed and a new denture made that can lock on to the implants.

Poli-grip is a good denture adhesive. A common mistake denture wearers make is that they apply too much of it. Follow these instructions:
A step-by-step guide to using denture adhesives correctly.