Alison, I would agree that Gentle Vinyasa Flow is probably the best bet for you.
All three DVDs follow the same format of two longer practices (ca 60+ minutes), and two shorter premixes of each. Each DVD therefore contains 6 practices, varying in length from 20-30 to 60+ minutes. Yoga: Flow has one practice which is 75 minutes in length, but as it includes (optional and skippable) chanting part, the physical practice is again just over an hour.
They all contain extras: GP and GVF have pose guides and YF has yoga nidra (guided meditation) and surya yoga (sun salutes practice with chakra related chants). I'm not really into meditation or chanting right now but they are separate menu options and are not forced on you in any way. GVF pose guide is very well explained.
I don't have GP (yet) but it looks like very basic, gentle, static yoga exploring and prepping for basic poses. I would still like to have it for a very light day but it might not be challenging enough for you, with modifications and slow easing into asanas (just guessing based on reviews and clips).
GVF is a slow flow consisting of mostly basic asanas. Practices A and B are similar in the choice of poses, but usually offer slightly different variations of asanas and practice B is a little faster (extra lunges with arching back are added to sun salutes/vinyasas) with the impression of continuous movement until you reach the seated poses section. I like practice A for its sequencing with tree and boat; the pace is just fine for a great soothing stretch with just enough of strength poses to feel a little "worked" too. It's very "simple and good" style. This DVD is my default practice, when I can't decide on anything else.
YF practices are in vinyasa style. They are not hurried but they definitely move. Like in GVF, the poses in A and B are similar, but practice A is a little more static with longer holds while practice B has more vinyasas throughout and also uses more "lunge, arch back" transitions to keep you moving. Compared to GVF Zyrka adds more balancing poses and backbends, also her standing flows are more demanding - longer and some have (optional) binds. For what you're looking for both full practices would probably be too much but the premixes tend to drop more demanding flows and might be a good match (if shorter).
I'm not sure why but I really love these practices. Zyrka is very understated but comes across as quietly confident and knowledgeable. I like her voice and choice of music. She doesn't overinstruct but she cues well and it's easy to get into the zone where your practice is smooth and focused with the instructor guiding but not overpowering you.
Well I hope it helps