@Marvy - Before I had my shoes modified by a shoe repair shop, I bought a gizmo on-line called 'Evenup' which was recommended by my PT. It cost about $35 with shipping. I think it's made somewhere in Ga. It fits over your existing shoe and comes with a lift of 1/2", and 1" so you can try both. I have one on a pair of crocs I walk in every day. I use the 1" lift. It's been on my croc now for 6 months and still going strong. Before thinking about lifts, it would probably help to first now the magnitude of your LLD.
As Pumpkin and Jamie suggested, a podiatrist can measure it. Some PT's are also trained to measure LLD.
As far as revision surgery to fix my LLD, I would never consider it. My elevated shoes work just fine.
Best of luck!