Abhyanaga is not the first thing that comes to mind. A well-balanced asana practice is likely to be more effective. Remember Patanjali’s order: yama-niyama-asana-pranayama-pratyahara-dharana-dhyana-samadhi. Do you go to a weekly hatha yoga class? Do you have a home practice in yogasana?
Some suggestions building up strength in the spine: cat/cow, sunbird=tiger (one knee to nose alternated with extended leg from cat position), rounding and stretching the back in a seated posture, sideways bends in a seated posture, twists in a seated posture, cobra (bhujangasana), locust (salabhasana) and extended triangle (utthita trikonasana). For the thighs (rectus femoris and psoas) add: warrior-II (virabhadrasana), upward stretched legs (urhva prasarita padasana), and stick (dandasana). Allow 4 - 6 weeks of practicing 3-4 times per week to see some improvement.
Always opt for the most comfortable meditation position. All you need is a straight spine and props are allowed (cushion, meditation bench, even a chair). Make sure you are comfortable and free from pain, otherwise you are contradicting the first yama (ahimsa). Another way to build up strength is to gradually increase your meditation time. From what you are writing, you may need to start with 5 minutes and gradually increase by 1 - 2 minutes a week. I’m assuming a daily sitting practice.
