B.P.
When my son was your age, I found myself in this same situation with nap time. What I found worked best for my son was on the days that I could tell he needs a nap I would lay him down for one. On the days where he seems to be holding up fine then I wouldn't put him down for one. What I found was that on the days he didn't take a nap, he would be ready for bed a little earlier then usual and eventually on the days where he would nap, he would have a hard time going to bed at night. Eventually we worked our way out of napes completly however I before we got to that point, I would play it by ear. For the days that he may not seem especially ready for a nap but maybe you need a break, then lay him down for a nap but give him another option as well. Tell him that it's nap time and that if he isn't tired then he can lay there quietly and read a book or color a picture but that this is quiet time now and if he's going to color or work on a puzzle that he needs to do it quietly and that he needs to stay in bed until nap time is over.
My son is 6 1/2 now and every now and then he will need a nap on the weekend, so this is always an option for them. If you take away the nap as a rule or as a part of your set routine and leave it open as an option if necessary then your son will still reep the rewards of getting a little rest on the days he needs it and on the days you need the break you can call it quiet time, where he can do a select few activities quietly rather then taking a nap.
Good Luck with this!