Stretches I do most commonly:
- Standing quad
- Standing hip flexor
- Downward dog
- Cat stretches
- Cobra
- Pigeon
- Child pose
- Knees to chest
- Figure 4s
- Straight hamstrings
For strength work, I do:
- Planks
- One leg planks
- One leg-one arm planks
- scissor kicks
- Bosu ball curls
- On hands and knees - one arm-one leg extended
- Side planks
- Side planks with one leg up.
I've never heard anyone say stretching was bad. I've been to orthopedists, chiropractors and physical therapists about my back. All encouraged stretching and strength work.
There's also a substantial body of literature arguing that athletes who injure their back should continue exercising, as it will help. I once tweaked my back right before a hockey game, and I struggled to get to the ice, but after the game, it was like it never happened. Of course, a lot of this research is tied to people who exercise in upright positions. I have not had the same experience with cycling, and lifting will make it worse.