The harness system works pretty good for the larger breeds. You can also use a large towel under the belly to help give him some support as he goes up and down steps. You often dont need to take all his weight, just enough to take the pressure off the hips.
When buying pups, be sure to check on the status of the parents. I personally will not buy a pup that does not have OFA or Penn clean hips for both the dam and stud. That is your best insurance against having to deal with hip dysplasia later in life. For some breeds, you want to be sure the parent stock also has clean elbows and retinas.