I am 50 and have a lot of physical ailments also. I have been in and out of bed restriction for the last 2 years and have gained 15lbs.I am 5ft 7inches and weigh 226 so I can relate to your situation. Food journal is the first place to start. I hate counting calories but when you know where all your calories have come from and how much it will take for you to burn those calories you will be less likely to eat them. Get into a pool and just move around for an hour three times a week. It makes you weightless so it is easier on the body and it's wet so you don't sweat. Start slow but just do something and you will be amazed at how the weight will start to come off. Use some soup cans in each hand and just move them up and down at your waist and above your head. Just move.
Are your physical problems due to your weight issue or are they medical problems?
Have you had your thyroid checked to be sure you don't have hypothyroidism? That only requires some simple blood tests for TSH, Free T3 and Free T4. You should also rule out insulin resistance.
You should talk to your doctor about what exercises you are able to do. You might look into chair yoga, which doesn't require standing, plus there are other types of yoga you could look into. Yoga is very low impact and there's a variety for nearly everyone.
Since you don't do any exercise to speak of, you will have to pay particular attention to what/how much you eat. Not being active decreases the number of calories/day you would need to eat.