Product review (5 stars): Washer seems fixed, after some additional diagnostic steps
This solved our problem, and since it'd been two weeks since the SUDS/F35 error had been seriously problematic, I splurged for the Amazon part to get Prime shipping versus waiting longer with other sellers that had more expensive pricing on faster deliver.  The packaging was labeled "Whirlpool" so it seems to be a genuine OEM part.  Before buying and installing this part, I had tried some other solutions based on what I read in these reviews, on YouTube and other forums, so a summary:
- Washer is a Whirlpool Duet Steam WFW9600TW01
- SUDS/F35 error occurred at the start of wash cycle
- ran the washer's diagnostic test cycle but got stuck at C00 (1st "gate" in the test program).  Searching the web should show you how to start the test, but I also found a yellow instruction/diagnostic sheet tucked in a pouch inside of the side wall, close to the corner by the pump, which listed the test procedure and program steps.
- based on a YouTube instruction, I checked the steam function, and it was ok.
- cleaned pump out drain located below washer drum; need to remove the panel directly below the washer door.  YouTube videos were very helpful for this.  I removed a lost wash cloth and ran the washer's diagnostic test again, progressing all the way through this time, but, still got the SUDS/F35 code when I tried to run a wash cycle.
- tried blowing out the tube connected to the pressure switch and jiggling the wires; still get the SUDS/F35 code.
- again, based on a YouTube instruction and the comments posted, since the diagnostic test completed successfully, I didn't think the CCU was the problem.  To avoid buying this more expensive pressure switch, I wanted to check the CCU capacitors, but I had trouble removing the CCU, so I went ahead and bought this pressure switch.

We've done about 4 loads now and it seems to be working normally again, fingers-crossed!