From what has been posted here with measurements, the difference between size 6 and 7 is now pretty minimal. From that, I wouldn't expend any major effort to get 7s. Personally, I'd go for diapers made for adults but if you think baby diapers are going to do it better for you, go ahead.
There's also this company to consider if you're really committed to baby diapers: https://www.convertups.com
Pampers make great boosters, but like Kryan said you need to stick with adult diapers that are made for your actual size and are way less likely to leak.