How to find out which backported packages are available, and avoid losing packages when manually upgrading?

How to find out which backported packages are available, and avoid losing
packages when manually upgrading?

I was surprised to see that since Natty 11.04, even when we have enabled a
backports repository, updated packages aren't automatically installed from
that repository. We have to install individual updates manually, e.g. via
apt-get install ipython/precise-backports
as explained at UbuntuBackports - Community Ubuntu Documentation. I guess
I just didn't get the memo....
First question: how do we find out what our options are for upgrades via
backports? I'm surprised that even if I ask for status, e.g. via
wajig status ipython
it doesn't tell me there is a new version available. I'd like a list of
all upgrades for packages which I've already installed.
Next, how do I avoid losing existing packages just because I upgrade via a
backport?
E.g. the above ipython install tells me:
The following packages will be REMOVED:
ipython-notebook ipython-qtconsole
How do I say I want the latest backported ipython, as well as any other
packages for which updates are available that depend on it, without
manually figuring them all out and installing them also?
I know I can change the pinning so that I get all updates, but I'm
hesitant to go against the general advice not to. But if a user asks for
one package to be updated, wouldn't it be natural to update all the
dependencies, like you'd get from a ppa?