Ankle circles. Both directions.
Pelvic tilts. Lying on your back, flatten the lower back into the mattress, hold five seconds. Ten reps.
Knee-to-chest. Gently bring one knee toward your chest, hold 15–20 seconds, switch. Three each.
Knees together side to side. Let both knees fall slowly to one side, hold ten seconds. Three each way.
Cat-cow on the bed. Arch upward, then drop the belly. Ten slow repetitions. The single most recommended exercise for AS mobility.
Neck movements. Slow, small rotations.

Getting out of bed: roll to your side first. Use your arms to push up to sitting. Sit on the edge for 30–60 seconds before standing.