You can do this by adding the entries for the Ubuntu repository to a file in
/etc/apt/sources.list.d. But you should not do this, in the same sense that while crossing a busy 6-lane motorway on foot is physically possible, it is generally not recommended.
Mixing repositories from different releases of distributions, even if these distributions use the same package manager, tends not to work well because the different releases have different sets of library versions. While Debian and derivatives (like most distributions) arrange to allow multiple versions of libraries to be installed at the same time, that doesn't always extend to other packages that sometimes depend on specific versions of the libraries. It might work for a while if you don't install development packages (development packages tend to have precise library requirements), but sooner or later you're practically sure to run into conflicts.
Library incompatibilities are why PPA have separate sources of binary packages for each Ubuntu release. Mixing a Debian release and an Ubuntu release is similar to mixing different Ubuntu releases.
If you want Ubuntu's drivers, the simplest solutions install Ubuntu. Low-level software (kernel, core system utilities, X server and libraries) tends to need to form a coherent whole. It's usually safe to install a more recent kernel, but you'll also need to install corresponding X video drivers, at least if you use proprietary drivers, and you need to have the configuration and sometimes patches that the distribution expects (and Debian and Ubuntu don't configure their kernel in exactly the same way).
As a user and as an administrator, there's not all that much difference between Ubuntu and Debian. Whatever reason you have to prefer Debian, if the latest Ubuntu has drivers for your hardware and Debian lags behind (not an uncommon situation if you stick to Debian stable), switching to Ubuntu might be best.
If you absolutely want to have some packages from Ubuntu and some packages from Debian — or if you want to have packages from different releases of Debian/Ubuntu (that's especially useful for developers who want to test their builds on different generation of software), it's fairly painless to install additional Debian/Ubuntu releases in a chroot, so you run one release for your system but can run applications from another release.