Janie,
You may have already tried all these ideas but :
On days when you are really bad off ( for whatever reason) just do a warm-up followed by the stretch. ( ex: Muscle Max, or Low Impact Circuit DVD) ( Or you can add in the core workout too. Then you have done a 20 min. mini-workout which is good for a whole lot of reasons.)
Good easier premixes are:
ICE-MTB-Pre-Timesaver #4 32 min
Cardio:
ICE-LIS-Pre-Timesaver #4 28 min
ICE-LIS-Pre-Timesaver #10 28 min
CrossFire-Pre-Timesaver-Low Impact Tabata 18min !!
TTM-Pre-Timesaver "No 30/20 HiiT " 40 min ( I modify the TABATA to make it low impact )
TTM-Pre-Less Impact
KPC- Pre-Cardio Conditioning 37 min
SAS-Cardio Slam-Pre-Timesaver#6 17 min !! ( I modify 2 exercises here )
Lower Body:
ICE-CLBB-Pre-Timesaver #4 40 min
RWH-LIHI-Pre #1 All Strength 30 min
X-Train-Cardio Leg Blast- Pre-All Strength 36 min
X-Train-Legs-Pre-Legs-Standing 29 min
GSL-Pre-Timesaver #1 32 min
SAS-TBGS-Pre-Timesaver #1 ( LB ) 31 min
SAS-PHA-Mishmosh Pre-LB Split #1 27 min
There are so many more, these are just some. I think it is easy to modify UB workout just by the amount of weight used.
A P.T. told me a few years ago that now is the time for me to do less 'compressive' workouts and vary things up with more yoga, stretching, swimming, biking. Most of these premixes are about 30 min, so I can use Cathe's premixes and add on core work and stretching or some yoga afterwards. That way I can still get my heart pumping and do a Cathe workout without the injury risk. ( Because I am spending less time doing "compressive" workouts.) My "endurance" workout is swimming once a week.
I don't know how much you have looked at using her Premixes, but they are so great for the very situations you mention. It is like having a whole new set of DVDs .