I have always had my leg length checked both standing and lying down by different orthopedic caregivers. This included chiro, many PTs, 3 different orthopedic drs, a spine specialist. They do you standing and see how your hips look. Most of them put their hands on my pelvis and seem to eyeball how level it is. Then lying down, they pull both legs until they seem to be in a natural state and eye ball that. They hold the feet both together closely to see if they are at the same distance and apart. I have never been measured with a ruler, so can't help you there.
I am not sure why your dr says your new hip will make your leg longer unless you have no cartilage in both like me. They have the ability to make some adjustment in leg length with the length of stem they use. I know for me, the mix up that caused my second surgery was when my surgeon did not like the length of the second leg with the ball that he used. He asked for a ball that added a little more lenght to the stem. Unfortunatly for me, he was given a ball made of an incompatable material to my stem!!
A small leg length discrepancy is not too bad, may people have it, but if it is enough it can cause lots of other problems, including in your spine. So I think I would talk to maybe a poditrist or someone that specializes in orthotics. I am surprised your surgeon can't refere you to anyone, but I would do some looking/asking around. Good, custom orthotics can make a big difference. I think you would want the kind that are made for you from cast imprint. You stand on a special foam block, both feet, and they make the orthotic to fit.
Congrats on deciding to go ahead with your surgery. It is a new lease on life for me!! If I can give you one word of advice? Get prepared as much as possible. Start now to get in as best a physical condition as you can. Make your body strong. Learn as much as you can about the procedure and what to expect. I 'trained' for my surgery, much like I train for an athletic competion and the payoff was huge. I set a hospital record for a bilateral stay (2 DAYS) and find my recovery to be a breeze.
Do you know yet what the approach will be and what material you are getting? Hopefully your dr will tailor that to your individual needs.
I definalty think I am slightly taller now, can tell when kissing hubby