Okay to use a queen flat sheet but not fitted esp. if the mattress is one of the "deep" mattresses. If not, even a NEW queen flat will be way too big.

Finding full-size sheets now is a challenge. Go on eBay and look at "vintage" sheets, blankets, etc. I need bedding because I rent my house, and the two places I get tenant bedding are eBay and HomeGoods, and I only get 100% cotton, or 100% wool.

Full size bedding is a hit or miss thing. If you order on line from jcp you can usually get what you need.

In terms of what matches what, it depends on how you make your bed. I have a comforter and bed skirt and cheap pillows from walmart which I stuffed into matching shams that stay stuffed. So when I make the bed, everything is covered...the sleeping pillows behind the sham covered ones, the comforter pulled all the way up over the sleeping sheets.

DH uses a bedspread so everything is covered there too including his sleeping pillows...he pulls the bedspread up and over the pillows, tucking it under in the front.

I suppose if you want to make your bed like a catalog, then you will want sheets that match or coordinate with the bedding, but I never really liked that as I figure the sheets just get dustier during the day...I'd rather have them covered. It looks great, but IMO is less practical.

I think you can mix and match solids and prints in the same color family...I.e.. Plain flat or fitted sheets with floral pillowcases or vice versa. I think you could also mix several plain pastel colors or bright colors. I wouldn't buy queen sheets for a full, but a queen comforter might work...don't a lot of them come in full/queen? As far as different "fabrics" I would be inclined to keep each set the same...all sateen or all percale, etc..

A queen is 6" wider than a full, so if you got a queen flat and didn't mind tucking it in, it would work.

I use king sheets on my queen bed all the time, even the fitted ones. I just tuck the excess fitted part under the mattress.

As for mixing and matching, why not? Some designers like Ralph Lauren mix and match patterns and textures purposely. Take a look at Ralph Lauren bedding pictures at Macys.com to get an idea of how the designer balances prints and solids and various fabrics. I agree with other posters that how much care you take with balance depends on how much of the various elements shows when you make your bed.

If I were on a limited budget, I would probably pay more attention to the quality of the materials, particularly the sheets. You can't see color or pattern in the dark, but you certainly want to feel comfortable when you sleep. Keep an eye on flash sales sites like OneKingsLane.com and Ruelala.com because they will often have sales on quality bedding.

I love vintage sheets and have bought a lot from eBay. Often, they are unused, but old. It's a little harder with Home Goods because sometimes name brands are duds. I usually try to check reviews on sites like Macys.com before I unwrap sheets from Home Goods in case that particular sheet was a bad fabrication. For instance, I think Ralph Lauren recently had a sheet that got terrible reviews and then I saw a bunch of them at Home Goods. I know from personal experience that Tommy Bahama sheets pill.

Real Simple has a good guide for buying sheets on their site. It's worth reading for basic information that may help you in your shopping. I'll link it below.

Here is a link that might be useful: Sheet Buying Guide

Don't forget places like Neiman Marcus--very good sheets and frequently on sale--and have lots of full-size sheets there. For me, it doesn't matter much what the bottom sheet is as long as they are in the same color or color family--but the top sheet and the pillowcases should match.
I recently "downgraded" to a fullsize bed and gave my Queensize to my son and ddl who are frequent guests. I use the queen size sheets on the full size bed from time to time, but there's really just too much fabric floating around. If I had the energy, I'd probably make up the bed with another flat sheet, which would stay tucked and tidier than the queen fitted. It gets very blousy on the sides and messy to sleep in. But, I'm a nut about how to make my bed.

You can use queen sheets on a full bed.

For the fitted sheet, you'll need to buy clips or elastic "suspenders" that will help to hold the sheet on the mattress. Easily found at stores like Bed, Bath and Beyond. Otherwise, the bottom sheet moves around and you get huge wrinkles under you, which can be uncomfortable.

For the flat sheet--I have a full bed and when I can, I buy a queen flat sheet on purpose. The extra width and length give you more fabric to tuck under the mattress, and it helps to keep the bed neatly made during the week.

Check out H&M and IKEA, surprisingly good quality and interesting designs.

And technically you don't need a fitted sheet. My mother in laws beach house has a total of 11 bedrooms! A few had kings and a few were bunk rooms with twins, all the rest were queens or fulls. It was the girls job when we were cleaning up to do the beds. All the queen and full rooms used white queen sheets and no fitted anywhere it was all in how you made the bed. It did make it easier to just grab a stack of folded white sheets and pillow cases and get busy.