The best available free-agent offensive lineman is easily Dalton Risner, who could come in and start for the Bengals if they were to sign him. Risner, a left guard, would give the Bengals a much better pass-blocker, evidenced by his 72.6 PFF grade during the 2022 season.
While Volson is fine, the Bengals shouldn't settle for "fine". Risner being available at this point means that Cincinnati could get the former Kansas State product for a much cheaper price and he'd have a chance to join a contender and potentially start in a Super Bowl.
For what it's worth, Risner was initially projected to earn a four-year deal worth $38 million, earning an annual salary of $9.5 million, according to Spotrac. It likely wouldn't cost that much to land him at this point of the offseason and the Bengals should absolutely see what it'll take to land Risner.