Firstly switch to shoes with a lower heel and if you can see a podiatrist to check if you need supportive insoles.
Try the Alexander Technique or Yoga as both these activities encourage better posture.
Buy a new mattress or mattress topper for your bed, especially if your mattress is more than eight years old. There are a number of different types of back pain support toppers available.
Try to lose any excess weight.
Check your workstation and seating arrangement. If you are sat at a desk all day a footstool may help or a supportive chair, or simply a rearrangement of your desk and monitor.