How bad is the HD in your dog? Have you tried less invasive methods of controlling the condition before opting straight for the operation? Especially in young dogs where the HD is not yet very severe, it is often a better idea to try and minimize the condition as much as possible with appropriate exercise and supplements in order to give the dog the longest period of normal life as possible.

I am not a vet and (more importantly) i haven't seen your dogs condition or the x-ray, however in less severe cases of HD especially if it is in a younger dog that may have suffered a lack of appropriate exercise or vitamins/minerals during part of their growth, an operation isn't always necessarily the best solution and (assuming your dog is not in debilitating pain) it would be worth exploring other options first.

Gentle exercise such as 5-10 minutes slow walking and especially swimming (as mentioned) is great for helping keep the joints supple without causing extra stress and damage. Depending on which area you live in there is Furrenz and K9 cottage as mentioned. Also KL Pooch Rescue has a swimming pool and also have experience with introducing dogs to swimming and rehabilitation.
Definitely don't allow your dog to jump or stand up and limit his walking up and down stairs as much as possible. These are all activities that put huge strain on his back legs.

As far as supplements go, any Glucosamine and Chondroitin combo will do. The initial dosage for the first month for a dog around 20KG with an existing condition is 1000mg Glucosamine and 500mg Chondroitin. After the first month you can drop the dose to as low as 500mg Glucosamine and 250mg Chondroitin if the hips seem to be loosening up. You can use the pill based supplements you find in pet shops, however it would be advisable to give your dog supplements daily for the rest of his life to minimize the chances of him needing an operation in the future, so it is actually more worth while going to the pharmacy and buying the biggest bottle you can find (make sure the version in the supplement you choose is "Glucosamine Sulphate" and "CHondroitin Sulphate" as this is the one safe for dogs).

Other methods of helping deal with HD include hot compresses on the joints, massage or physiotherapy and acupuncture to name just a few. There is a very good canine acupuncture therapy in KL (although her name escapes me right now) and also a lady who does canine physiotherapy in her spare time (she is not professionally trained but has had some great results in a number of cases).

That is quite possible. Sounds right.