We suggest buying a helmet with standard width straps, not the skinny ones. You can add little rubber bands or o-rings to the straps to slide up against the buckle when it is adjusted right. And after you get your helmet adjusted perfectly, you can sew the strap ends in place. You must replace the helmet after any crash where your head hit. The foam part is made for one time use, and after crushing once it is no longer as protective as it was, even if it still looks intact.
Plastic shells can hide the foam damage.
A few helmets made of EPP foam do recover. If in doubt, contact the manufacturer for an inspection. If your helmet is more than 10 years old or has a cloth cover, we recommend that you replace it. Many manufacturers recommend replacement every five years, but some of that is just marketing. Deterioration depends on usage, care, and abuse.