Yes, I agree with the recommendation for Waitrose flowers. I use them as my florist of choice and they have never let me down.
I understand the recommendations for other things, but I always find that there is nothing like the mental lift and joy that opening the front door and being presented with a gorgeous bouquet of flowers gives me and especially as your relationship is a little prickly.
Flowers, is flowers, is flowers, all sorts of unintended motives can be read into a gifts of food and other things. For the same reason, if she is home to receive them, I think a bouquet of flowers at the door, is so much better than letter box flowers.
Everything has its place. I have sent food and letterbox flowers and they were the right thing in the right situation, but in this case I would really go for the bouquet at the door.