You shouldn't have a problem with drivers or anything else since your laptop originally came with Windows 7. The same drivers will be used for Windows 7 Home Basic and Windows 7 Ultimate (and all versions of Windows 7 for that matter). You will be able to simply download the drivers from Sony and install them on your new OS. If Sony is being a b** about their drivers (which is possible) then it is always possible to unzip them from their installer package and install them manually. I do recall doing that more than once on my Vaio desktop when I installed a retail version of XP versus the OEM version it came with.
In summary any issues you might have installing Windows Ultimate are minimal and can easily be worked through.
On a side note I haven't seen any major usage differences between Windows 7 Home Basic and Windows 7 and any other version of Windows 7. If you looking for more features such as Media Center, BitLocker, etc., then upgrading might be a good idea. If you simply hate the look and feel of Windows 7 Home Basic then I wouldn't bother upgrading.