Blue Grapefruit is quite right - sole source is sole source, and that's that. But if you don't want to stick to sole source, then do Sole Source Plus or anything upwards, calorie-wise.
As far as pre-cooked, shrink-wrapped chicken is concerned, it's extremely unlikely to be 100% chicken. Last packet I looked at was 83% chicken and a load of fat, salt, sugar and flavourings.
Just buy a pack of raw, skinless, boneless breasts, cook them all according to the book, slice them thinly, and freeze individual portions until you need them - easy, cheaper and you know what you're really eating.