It sounds like you are trying to enforce a rule that has been ignored.  You will find resistance out of sheer refusal to change behavior. In my experience, having visible upper management support helps tremendously with the laziness related excuses.  This visibility could be direct or indirect in the way of:

e-mails,

from upper management or where upper management is on the CC box

short meetings

scheduled and opened by upper management, but where the floor is yielded over to you for the majority of the meeting time

new door signs

                PPE required beyond this point

                googles and lab coat required beyond this point

no food or drink beyond this point

                revised/updated safety program

consider adding a statement at the beginning of your written program reinforcing the requirements for wearing PPE at all times inside labs

Outside of laziness issues, I agree that most non-compliance is related to proper fit. For the most part, people want to wear the necessary PPE and will happily comply with the rules if the PPE fits.

However, I have seen situations where the PPE selection does get in the way of the work. So, you have to re-evaluate and adjust the PPE selection. I did once have a situation where hygiene was a real concern with shared gloves. So, we bought disposable glove liners to reduce sweat issues with the shared gloves.