But you lose the "happiness bonus" points that comfy beds give you though (how many bonus points, nobody knows). In my early levels I also used sleeping bags only. But later I ended up having to build more spacious houses just to accommodate the higher level beds. Beds are probably one of a few things you build the most of, so you risk losing a lot of happiness points if you don't build the best beds.
Regarding OP's question about scarcity of resources, it's true even when I'm up to level 60. Trees are everywhere, so getting wood is not a concern. But I'm often low in steel, which is the other most often used resource. There are only so many cars and barrels you can scrap. Naturally, I build mostly wood houses as opposed to steel ones. There are some settlements where I only scrap things and never build anything, just to get some free resources. Other than that, I have to get steel the hard way: looting buildings and dungeons that I've already looted before. Copper is another resource that can run low, but it can be easily had by scrapping pipe rifles (which are abundant) with the Scrapper perk. Oil can run low too, and you need to craft cutting fluid at the chemistry station to get it, which means you need to get purified water, bones, and acid. You get purified water automatically put into your workbench if you have more water than settlers. Acid is found in abraxo cleaner so it is ubiquitous. Bones are a bit less frequently found. I know there are oil cans and stuff where you can get free oil, but from my experience that's not enough. In short, wood, steel, copper, and oil are the things I have to actively put an effort to find. I know weapon & armor mods need rare resources too, but curiously, mods are one thing I make the least. If you make a really good weapon or armor, it usually lasts a long time.