From you description you have Osteoarthritis of knees. This is normal ageing of the joints. The decision to operate or not to operate is to a large extent dependant on your symptoms. If you have severe pain on movement, difficulty in walking and your activities of daily living are restricted then you can decide regarding the need for an intervention. The decision for surgery in not based on X-rays. X-rays help the surgeon in confirming the diagnosis and planning for surgery. The decision to operate is purely on clinical grounds. So, if you are able to walk without too much of pain, I think you could easily wait and try exercises along with occasional paracetamol. If you need to take pain killers regularly to work then again re-consider your decision.
A doctor may recommend surgery based on clinical evaluation. Is usually guided by:
The pain that you have on movement of the knee joint.
The deformity that you have it is difficult to do exercises with a grossly deformed knee in such situations (even here only if you are uncomfortable) surgery may be advisable.
If there is instability of the knee where every time you put weight on your legs the knee joint gets further deformed. This leads to rapid deterioration of your knee demanding an early surgery.
Whatever be the combination of symptoms / objective signs the final decision is based on you as a patient and your difficulties in walking and doing activities of daily living.
You have asked a question regarding simultaneous total knee replacement. This is a hugely controversial issue in orthopaedic surgery with proponents for and against almost neck-to-neck. In countries where costs of surgery are borne by insurance companies there is a distinct bias towards bilateral total knee replacement. This is because the insurance company has to pay for single admission, single anaesthesia, single consultation, single physiotherapy and medication for both the knees. It is estimated that it reduces the cost by around 50-60%. Naturally sheer economics wins in this situation. However, scientifically it is not an open and shut case. There are arguments that the rehabilitation required for a bilateral simultaneous total knee is longer than for a staged unilateral knee replacement. In fact there are studies that report that bilateral total knee replacement needs longer hospitalization. Other outcomes are reportedly similar. But there are concerns that the prevalence of complications like deep vein thrombosis (clotting in the veins) and pulmonary embolism (clotting in the lung veins) is higher. There are other similar concerns however the debate is not yet resolved. The consensus seems to be that if the patient is older than 80 years there is a slightly higher risk for complications in simultaneous bilateral total knee replacements. There are also reports of a staggered knee replacement in the same hospital admission with a gap of 4-7 days between the two sides to reduce some of the anticipated complications.
Not withstanding the discussion as above, once the decision for replacement is made, I think you should leave it to the wisdom and experience of your operating surgeon. My personal bias is for a staged unilateral procedure.
The current prostheses that are available are all technically advanced and I do not think you need to worry about their quality. The price difference is also not substantial but if you have significant deformity or other technical problems, then additional attachments may be required for the components and these may push up the cost.
The approximate time to walk with support of a walker is about two days. We allow the patient to walk with support anywhere for 4-6 weeks. By six weeks we expect the patient to walk independently, though this may take slightly longer or shorter in some cases.