Option 3: Derrick White
Another viable option to fill the role of backup point guard could actually be Derrick White. While he is likely to continue as a starter next season, coach Popovich could stagger Murray and White, allowing him to also play with the second unit. White would provide similar (if not better) defense compared to Jones while not being a liability on offense.
After all, Derrick has plenty of experience playing with the bench. Playing with the reserves would give him the chance to be the primary shot creator for stretches, helping ensure that the bench is able to score consistently. That said, we've already seen that he's also capable of being the team's floor general and creating for others.
It would also allow Popovich to choose from a number of lineup options. If Thaddeus Young were to come in as the unit's small-ball center, Luka Samanic or Jock Landale could come in as the bench unit's power forward. Popovich could also play either Forbes or Jones alongside White, Walker, Vassell, and Young. In my opinion, in this situation, Forbes' ability to play off-ball would likely be the best fit.
Ultimately, White is a bit of a Swiss Army knife that can fill in whatever is needed in a given lineup. Moving him to the bench unit could given both the starting and bench units more balance and flexibility that was not experienced this past season.