People make oil consumption a bigger deal than it actually is. Burning 1/3rd of a quart in 18 hours sounds like a lot until you consider that the average residential mower will accumulate 50 or so hours per season, meaning...you'd have to add one quart per season.
Also, engines can be finicky not only about weight, but also brand of oil. I bought a used C-50 Chevrolet truck from a guy who told me to run Conoco 30w in it. I didn't have any of that and was running Quaker State in everything else, so I switched to QS. It guzzled the QS. Switched back to Conoco and the oil consumption went WAY down. Also had a Ford Ranger with a 4-banger engine. The book recommendation was 10w-40, which it consumed at the rate of about a quart every 700-800 miles. Switched to 5w-30 and it would then use a quart in about 3,000 miles.
Sometimes it pays to experiment.