Unless you live with your girlfriend/mother, there's a good chance your apartment's so cluttered and shabby, both your girlfriend and mother deny your desperate pleas to sleep over. For home design that's ridiculously affordable, try HomeRefiner.
Run by a Belgian-born, passably attractive (see photo) HGTV expert named Elfya, HR's an interior design firm that handles everything from painting schemes to furniture purchase/delivery/installation -- all you need to do is stay strong when your "Sweet Chaise w/ Cupholder" gets returned to the swimming pool from whence it was stolen. For only $75, Elfya'll provide a one- to two-hour consult, ferreting out your likes (favorite color, etc), lifestyle (whether you throw parties), and budget, then break out look-books stocked with furniture and color samples she'll match with your personality (if you're still in your "Hooters Deathstar" phase, call her back in five years). With an eye towards storage, she'll suggest affordable options from boutiques and familiar retailers (Pottery Barn, etc), then suggest easy customizations, e.g., disguising crates as ottomans, and draping fabrics over shelving to reduce clutter/the chance visitors will see your collection of Pottery Barn catalogs.
For those seeking a complete overhaul, Elfya offers more comprehensive services, from installations to re-drawing floor-plans. If you're up to DIY'ing, she'll also put you in touch with vendors directly -- though if you had that kind of initiative, your mom would even now be calling your sleepy-eyed girlfriend a shiftless harlot.