Hand-me-downs, estate sales, craigslist for the materials. Apartment Therapy, Design Sponge, and Emily Henderson for the aesthetic. :)
Seriously: We have a 3-story house, and we have bought new 1 mattress and bed frame, our appliances, and a lamp, and soon a new sofa. Everything else is from the sources listed above, and we consistently get compliments on our house: we've had artists ask to set up photo shoots for their work in our house because they thought the decor would set off their paintings and prints well for online sales.
You don't have to get junk because you're buying used... but you're within 5 years of my age, and this is totally the time where people our grandparents age are liquidating their houses, and a lot of people don't want a huge oak dining table with 6 chairs and a gorgeous buffet (a friend recently acquired a set like that from Kijiji: 500$ total. We got ours as a hand-me-down). Bedroom furniture from the 40s and 50s is MUCH more solidly made than new ones - you can generally get gorgeous teak dressers from that era on Craigslist for the same price as new Ikea, and it's way more solid, has way more personality, and if you get sick of the aesthetic in 10 years it won't be near-worthless for resale like the Ikea stuff will.
Mix antiques with more modern stuff, add textiles (rugs are great, but also pillows - learn to sew the pillow covers and save $$ - and curtains), and art, and you're seriously getting somewhere.
NOTE: some things are worth buying new if you can't get them from somewhere you know. The nearest city to where I live has an epic bedbug epidemic, so I inspect all wood furniture closely, bought my mattress new, and inherited our basement couches. Mattresses and soft furnishings are especially suspect. But, to your point about beds: buy the mattress and box spring new. Wait for a month until you spot the bedframe you like on Craigslist. Or buy a 50$ metal base and search one of the (many, many) Apartment Therapy tutorials to make your own headboard for very little - the headboard itself is mostly for the aesthetics, anyway.