I'd really try and have a look into making your own. I think one reason why wraps are so popular in sandwich shops is that they can get away with putting hardly any filling in them.
When you make your own wrap, you realise that you can't put a lot of filling in, as it won't wrap properly.
I fell in love a little bit with their falafel and halloumi wraps, but I don't really have a convenient Pret, so started making my own. After I'd had a few of my own, which really were very quick and easy - I just kept falafels in the freezer, we always have several packs of halloumi in the fridge, plus whatever leaves and relish/pickle type stuff seems appropriate, I had a Pret one again and realised that mine were so much better.
The once a week thing seems like a good idea. That way you're cutting down significantly but not missing out completely. Of all the things that lunch type shops sell, posh salads might be the best thing to get, as its a faff to do all the different fillings, dressings and herbs, unless you are making several portions.
Miso and red Thai soup are fairly easy to make for a fraction of what Pret charges. Can you take it in to microwave at work?