My DD only ever cat-napped for 20 mins too. I remember going to Mothers Group and all the other babies were sleeping 2 hours or more and I felt like killing all the smug bi-atches! But DD grew out of it eventually. Still doesn't do enormous sleeps, 1.5 hours during the day is generally her limit.

Have you tried white noise? I'm just throwing out anything that you could try as you seem to be doing everything you can. DD loves having her radio on even now (on a fuzzy non-station) and it seems to block out other household noises too so she's not disturbed, but still soothing hum to it.

Other than that, perhaps try the gin for you?

Want to come over for a play during the school holidays and maybe I could have a cuddle just to give your arms a rest?