Hi, I would recommend biology!
I did the same A-levels as you and also had the same interests, and faced a similar dilemma. I started out doing a zoology degree, and had the to option to switch to biology after first year as the first year was the same for all the biologists and zoologists. I switched to biology for the sake of having a broader degree, and was glad I did. I was still able to tailor my degree to ecology, behavior and conservation, with one plant module thrown into the mix. It has helped me in my job hunt after uni, as my new jobs requires some plant ID skills!
With interests in the environment and conservation, it's really good to have a good grounding in botany, including evolution, invasive species and pollinator networks.
It's definitely important to look at the specific modules of the course. I never realised how much biology degrees could differ between different universities until I was at uni! It's worth visiting as many universities as possible to look at the facilities and the research interests of the lecturers.