Are you allowed fasten things to the wall? Kitchen cabinets mounted under the window provide serious (and sturdy) birdwatching potential – and some extra storage space.
Swap out a cabinet for an open shelving unit. Room to sit, and easy-access storage for your chosen method of entertainment while you’re sitting there.
This combination of two footstools with a small stool in between would be perfect for tea or coffee for two, and a gossip about the delivery people driving by.