Try a raised flower bed. These are the perfect way to keep from bending several times a day and creating fatigue. Make sure you don't forget that straw hat to stave off heat exhaustion. The perfect height seems to be just to your fingertips when you are standing.
Step2
A centralized water bucket keeps you from lugging heavy containers to and from while you water your plants. If you can afford it, install sprinklers for centralized spraying. This also is a money saver. Sure there is a moderate payment, but it cuts down on your bottom line by watering more efficiently. Keep an eye on the weather too, so that you don't spend the afternoon watering right before a rain.
Step3
Think perennials, shrubs, and trees instead of annuals. With proper mulching program to stave off weeds, most perennials can be a plant-once-and-forget deal. Plus, perennials can be used as a money saver by dividing it and using it throughout your landscape or garden.
Step4
Don't forego the mulch. A small layer of newspaper under the mulch of choice will also provide an organic biodegradable landscaping fabric. Mulch will break down over the season and will help enrich the soil. It may sound like less work to not mulch your garden, but you'll lose out and have to weed all bloom season. Also with any leftover mulch, consider making a compost pile. Rich humus will be yours all next season.
Step5
Buy one of those cheap tool aprons to carry your small ergonomic garden tools with you so that you don't have to make so many trips or bend as much to pick them up. You can also consider a small child's wagon to roll around your plants so that you don't have to carry them. This may seem a bit lazy, but remember that you can garden longer and get more accomplished when you aren't as tired.