there are really lots of options open to you here. for example, the 35mm is a great street lens on a crop sensor, will work also for landscapes depending on the angle of view you want. I really dont see the need to fork out all the 500 quid to fulfil the needs you have specified here. For example, bearing in mind you will keep the 35mm 1.8 which will work for landscape, street, portraiture and low light, any of the suggestions from @
Horoscope Fish could be good choices. If you dont need the long zoom range how about the Sigma 17-70?
See if you can get along to friendly Joe at your local camera store and try a few lenses and see what suits you. In any case, and I am sure you know this already, avoid AFD lenses as they will not auto focus on your camera.