Lilly
Adult Guinea Pig
Diet is my biggest worry and I agree with your vet, nuggets when I think about it are a strange one. I feed mine in moderation and they get tonnes of grasses, unlimited hay and veg - mostly lettuces, kale and strawberry leaves. I am trying to get their diet correct in my mind and like you have read so much about it. In response to others where can you buy this oak lettuce? I've found sainsburys tesco and Asia are terrible for variety of lettuce, morrisons is slightly better but anything a bit different and supermarkets seem to not want to try!
I don't know which grocers in the UK stock the oak leaf lettuce. Perhaps you could ask in a thread of your own so more UKers will see and answer. Here they are sold everywhere. I've also lived in New Zealand where they were common but there they were called hydroponic lettuce.