1997 Saturn SC2 Trouble codes PO133 & PO141

Hi all, new member here. Recently bought a '97 SC2 1.9L 5spd 119K miles. And have to pass emissions to register it. Car runs good, but MIL light is on and throws codes PO133 & PO141:

O2 Sensor circuit slow response b1s1
O2 Sensor Heater circuit b1s2

I have AutoTap's diagnostic tool and have checked the IAT sens and ECT sensor. Both are operating properly. O2 sens b1s1 in the exhaust manifold oscillates, but does not hit the recommended low/high voltage output of.2 &.8 volts (should be replaced, but it's working) - O2 sens b1s2 behind the cat. Starts out with a voltage output of ~.7 volts (cold start), oscillating +/- 100 mV or more. As the engine & cat begin to warm (at idle), voltage output slowly drops. Getting as low as.35 volts (oscillating between.3 &.4 volts). Revving the engine to 2000 rpm and holding - the voltage slowly drops to a mere 150 mV and stays there. Even when rpm's are returned to idle.

From what I have found online, it appears that O2S B1S2 behind the cat should start out at a higher voltage of.8 to 1 volt, (cold start/rich condition), then as the engine/cat/sensor warms to operating temperature, the voltage should drop to approx.45 volts and stay in that range rather steadily (no wild fluctuation/oscillating as is the case with O2S B1S1 in the manifold).

Since my downstream Heated O2 sensor is oscillating (which it should not be doing AFAIK.) And, it's voltage output steadily drops, eventually leveling off at a mere 150 mV (instead of maintaining a fairly steady.45'ish volts). Do I replace this sensor first? Or could something else be giving me these readings? Bad cat perhaps? Or, could B1S1 be skewing S2's readings? Or, is there something else I am not thinking of, or aware of that I should be testing/looking at?

As I said - Engine temp sens & Intake air temp sens are working properly. MAP appears to be good. Fuel trim appears to be within proper limits.

If the cat were bad, wouldn't I get codes specific to the cat? (An oscillating O2 B1S2 can be an indication of a bad cat.)

My gut says replace S2 first. Then reset the MIL. See what happens. What do you all think?

I'm kinda missing those old CTO switches and vacuum operated emissions controls of yester-years lol.