Hi Lin,
I used protein shakes. I have precious little muscle tone as it is and wanted to avoid muscle wastage completely. This is a side effect of a low protein diet. I calculated that I should consume around 80g of protein per day, and I wasn't getting anywhere near that from food alone, even on a low carb diet. I used foodfocus.co.uk to calculate my intake.
Protein is important to weight loss, it keeps you fuller longer, maintains a good metabolism, maintains your blood sugar, and is crucial for muscle maintainence and repair. Carbs break down in the stomach very quickly, cause blood sugar spikes and dips, cause carb cravings, and offer far fewer nutrients.
Now that I'm farther out, I don't use them anymore, as I can consume larger quantities, and therefore get all my needs from food alone.
In the first 4-5 months post op, you can get away with eating whatever you want basically, and still lose weight. I call this the carb and cr@p trap! You can easily get in to bad habits, particularly with carbs and slidey foods like crisps. After this point though, unless you are following the post op rules (avoid drinks with meals; 2 bites protein to 1 bite other; eat protein first, then veg then starches last; avoid snacking between meals; avoid food habits like comfort eating) your weight loss will rapidly slow down and eventually stop.
As for where to get them from, if you search the site there are a few good threads listing types and suppliers. In general, look for atleast 20g protein and less than 3g carbs per serving.