We lived with my Mum and Dad until DS was 2, when we moved to our flat. We talked about it before, and visited the flat together a few times beforehand (not so easy for you!) and he was fine. The only thing was that for the first few weeks he would follow me about more, and he wouldn't go into a different room by himself for some reason. If he wanted a toy from his bedroom I would have to go with him. He wasn't upset about it, just insistent

I would talk about 'when we go to our new house' as much as possible, which you're doing already, and as Jenny said familiar items will help. Perhaps the same bedding?

As DD is very secure in her relationship with you I'm sure she'll be fine.