1. Do other things to improve your flexibility. I do gentle yoga on a daily basis, and visit my chiropractor at least once per month. This keeps me strong & flexible even during the winter months, when I can’t get out in the garden. What you do outside of the garden is as important as what you do in it!
2. As well as specialist back saving garden tools definitely do buy some knee pads and a tough pair of gardening gloves. While I use a weed-puller for most of my weeding, there are some pesky plants which need a more personal touch. For those weekends I actually have to get up-close and personal with the weeds (and also for thinning), I do the work on my hands and knees, which allows me to keep my spine reasonably straight and doesn’t put undue stress on my muscles.
3. Lift smart! If you have a spouse or significant other who is as crazy about gardening as you are, have them help out! Unfortunately, my husband is more of an indoors kind of guy. He helps me when I ask, because he loves me. In return, I try not to ask too often. This means using some smart techniques like moving my large potted plants with a hand truck, and never filling my wheelbarrow too full.