We have four greyhounds (all middle aged or elderly). I also do a lot of homechecking/voluntary work for greyhound rescue. I'm going to disagree with a lot of the previous posters who have recommended a greyhound -yes, they sleep a lot, but they still enjoy and deserve a decent amount of exercise.
To give you a picture ours (youngest is nearly ten, eldest is 13) have on weekdays an hour's walk or thereabouts, usually with some off lead time included in that. On weekends, walks are often longer, up to two hours. We also regularly participate in sighthound playgroups, sighthound agility, group walks, plus we take them to dog shows, meet and greets, etc. In addition to all that, they also go to dog training classes in rotation and we do practising at home (mostly using clickers). DH goes running as well, and will quite often go for a nice jog round the neighbourhood with one of ours. We live in an suburban environment with easy access to the coast and a variety of nice weekend walks e.g forestry, beaches, country parks etc.
OK, so you might not want to do some of the activities/social stuff, but I think our exercise regime is quite light. If I was doing a homecheck, I'd expect someone to commit to either a longer single walk (min. 1 hr) each day or at least two walks of between 20 and 30 minutes or combo - say one 20 min and one 40 min. It doesn't necessarily have to be you doing the walking - e.g. could be a dog walker on some days but if you couldn't/wouldn't manage that, then I think a lot of rescues would probably have a question mark about your suitability to adopt. Our senior boy has mild arthritis (which we are managing well) but he is fit, healthy and active with excellent muscle tone. Importantly, we also make sure he has a varied walking routine and doesn't just plod round the same route every single day. Yes, greyhounds are not border collies
but that doesn't mean they can't enjoy and cope well with a good level of varied exercise and training.
You might find it worthwhile to try the Oldies Club - a rescue which specialises in older dogs - there could be one suitable for you with lower exercise requirements.