If your beds have no solid bottom - just the native soil underneath - then you just want to fill with more native soil. Or moderately enriched native soil (additions of compost, composted manures, leaf mold, etc.). No peat moss or vermiculite, etc. Those are container soil ingredients. The mineral soil (regular garden or topsoil) element is critical.

Often, folks just do not have enough extra native soil available in their garden to fill a raised bed. The options then are to located a bulk soil or landscape supply yard and bring in a load of topsoil (which you can enrich just as you would your own soil). Many times theses same places offer a garden or landscape soil mix that has already had some sort of organic matter added and that works great as well.

You can also purchase bagged raised bed soil from various vendors but unless your bed(s) is tiny, that is not cost effective. A standard sized 4'x8'x10" raised bed holds right around a cubic yard of soil. Bagged raised bed soil is typically sold in 1 cubic foot bags...sometimes 1.5 cubic feet. As there are 27 cubic feet to a cubic yard, you would need about 25-27 bags. At roughly $7 per bag, that's pushing $200!! A cubic yard of bulk garden soil sells for around $36-40 in my area, less for just "topsoil". That's a rather substantial savings :-)

Our local nursery sells soil for filling raised beds. It's basically a mix of their compost and potting soil. They sell it by the pickup load, which is cheaper than bags and bags and bags . . .

The best way to buy compost is to first establish that it has been produced responsibly. Whether in sacks or piles, make sure that the compost is compliant with Organic Materials Review Institute (OMRI) standards. OMRI compliance assures that the compost is all biodegradable material, and any manures are processed to eliminate possibility of food contamination. I believe persistant herbicides aren't explicitly banned by OMRI yet, so you have to be careful about this if you're just getting it from some farmer who may not have a clue about them. If you get it from a local nursery, you're almost certainly good to go.