I find stretching incredibly boring but I realise how important it is, so I do Yoga up to 3x per week. I find all the hip opening exercise offer the most noticeable benefit but the 'pigeon pose'' is my favourite for really opening up the pelvis and relieving any strain on the lower back. As previously mentioned, hip flexor stretches are equally important. Search for Yoga stretches on you-tube, try them all and find the ones that bring you the most relief. But frequency is the key to long term relief.
If your job involves long periods of sitting, this often causes the most damage long term as it causes the hip flexor muscles to shorten which places added stress on the lower back which only serves to aggravate many lower back injuries.