Have you ever tried spinning? It can give a really intense, low impact workout. With any weight loss regimen, however, the cold hard truth is that diet is about 80% of the equation. I've recently broken a long plateau by significantly reducing my calorie intake. The first couple of weeks were really rough, but after two months I'm seeing some significant improvement for the first time in longer than I care to admit.
One school of thought is to eat 5 to 6 small meals throughout the day instead of the traditional three meals. The idea is to keep your glycemic steady and to prevent yourself from getting so hungry that you overeat. However, I found that my food intake actually increased when I was following this, so I've gone back to three meals with nothing in between except for a snack of some fruit and yogurt in the evenings because that is when I tend to be the hungriest.
What I would do is:
1. Look for some areas of your diet where you can cut back on calories by either eliminating certain things or finding healthier options.
2. Arrange to eat the bulk of your calories at the time of day when you tend to be the hungriest. I find that eating a very small breakfast (about 130 to 180 calories) and a moderate calorie lunch allows me to eat more calories later in the day. I know this goes against the conventional wisdom, but it works for me.
3. Let your Achilles tendon heal and try to work in some low impact cardio that doesn't aggravate it further.
Getting started can be tough, but if you can persevere through the first two weeks or so, it gets a lot easier, and once you start seeing some results, it gives you the incentive to continue.
