Yep, number one advice is to stay away from hatchery stock at all costs, and try and aim for true show quality or imported stock. And by show I don't mean the local fair or 4H. You'll be surprised, because even the average "Buff Orpington" people have are very, very small compared to normal Orpingtons found in shows. The average backyard laying hen probably weighs around 4 lbs, while the standard for most heritage/american breeds asks for 7+ lbs. That is a big difference.
That being said, if you want big, some breeds to look into are Jersey Giants, Cochins, Orpingtons, Langshans, Brahmas, Malays, and Plymouth Rocks. Real ones.
Funny thing is, even the so-called small breeds like Polish are bigger than most laying hens. Just last night a lady who bought some chicks from me last year was telling me how big her Polish rooster she got from me was compared to her other chickens! (average barred rocks and black sex-links) Which is funny because Polish normally should weigh about 4 lbs less than true Rocks.