After Illness

I've been rowing 2 million m a year for the last four years (a bit less before, but a long time rower). Could do 2 min/500 no issues, but that has dropped a bit as I've aged (68). Recently gone through a four week pulmonary illness that knocked my socks off and have totally lost my routine. I know going back to my hour three of four times a week is fruitless, so I'm taking it easy and trying to work my way back. But, I'm impatient. Any good advice on how to get back to my reasonable level more quickly?