Jazz was promoted to our bed from about 5 months - she'd been able to go through the night from a fairly early stage (@ 10weeks) so we could have let her on earlier. I put the soft puppy bed from her crate at the end of the bed and that's her place to sleep -I'm not sure if it helps with the connection of not peeing in her own bed or not but it gives us a bit more space!! She's also very good at waking us when she's been unwell and needed to go out at night.
If my in-laws are dog sitting we let them sleep in our bed (which is a super king size) so they can also have her on the bed-she's thoroughly spoilt!!