Ideological rankings for the 118th Congressional generally aren't available yet, but
this one for the 117th had Scott (R-FL) as the most conservative, followed by Braun (R-IN), Cruz (R-TX), Blackburn (R-TN) and Cramer (R-ND).
The median (#50) senator under this ranking was Murkowski. 2022 seems to have been an exodus of moderate Republicans, as Portman, Shelby, Blunt, Burr and Toomey were all rated among the body's most moderate senators.
Romney, Sinema and Manchin are retiring in 2024, and if Tester loses then the remaining "moderate" coalition in the senate is Murkowski, Collins, Kelly and...Warnock? (defined as senators ranked between #45-#55 in the ideological scores for 2021-22.) These scores may not accurately reflect how Kelly and Warnock have been voting since 2022, since they're now somewhat freed from election-year pressures.
In 2025, it will be interesting to see what kind of senator Fetterman becomes. His positions are heterodox enough that he can be usefully deployed to be the "fall man" for the moderate bloc. Ditto for if Hogan somehow wins, too.