Hip osteoarthritis, surgery needed?

I have mild degenerative changes in left hip, with joint space narrowing & marginal osteophyte formation, What does this mean? Had on the right side and needed hip replacement.

I don't have much pain it is just my motion is getting more limited

I've had both my hips replaced in separate surgeries. I had the worst one done first in the hope that the other one would settle down although the surgeon said that the xrays indicated that "I'd need both of them replaced some day". You have described the classic xray indications of hip osteoarthritis. Maybe you'll get lucky and it won't get bad enough that it limits your activities and causes pain. Or maybe you won't. Odds are probably not in your favor but who knows?
You have the dubious "luxury" of having been there and done that. What the xray report indicates is that you are probably on your way to another THR - when, only you will be able to determine. When the condition of your left side begins to limit your activities, you'll know that it's time. Since you are already aware of how well hip replacements work in terms of how they relieve pain and restore function in an arthritic hip, you too may be ready sooner this time. It takes some people longer than others. I waited forever to get my first hip done. Just couldn't get my brain wrapped around the concept of me needing a hip replacement. The second hip - well I had it done sooner rather than later. One good hip wasn't enough - I needed two!
Luck to you.

It means that when the pain gets too much to bear, then the hip must be replaced.

This is something to discuss with your orthopedic surgeon. Each patient is different (and your two hips might be different!)

He/she can give you the pros and cons of if and when to get the hip replaced. You already know what is involved, having had the right side done. Implants don't last forever, so many surgeons like to wait as long as possible to avoid the need to replace the replacement later on.

Good luck with the hips.