There's loads of scope within ecological consultancy to do work with plants and survey for interesting plants and good botanists aren't that common (in my experiance) I did a degree in biology (which would also then give you scope to get into micro biology or genetic studies with plants which you might find interesting once studying and that might get you into dream jobs at places like Kew Gardens or the Eden project).
Otherwise a more ecology related subject would be good (I did biology specialising down into ecology).
I can't speak for geography but I expect there's plant related stuff there too?
In relation to staying at home it definately helps financially, but when I went to uni well away from home it properly opened my eyes to real life, I learnt to support myself, cook for myself, pay my own bills etc, and finally I was no longer the geekey one because most of the people I was studying with loved the subject too!
I would also then recommend living away, your family will still be there and you will be dragging yourself home with a tonne of dirty washing every holiday anyway