I built nine raised beds this year out of those decorative curved edge concrete blocks that you just stack without mortar. They look really nice and I am delighted I did it, but it was not easy. First, they are heavy. Each one weighs 25 pounds,so I got a real workout and had to be careful of my lower back. But, the difficult part was getting them level. You have to level each brick from side to side, AND from front to back, AND it must be level with the one(s) next door to it. You cannot scrimp on this or your beds will look awful. It's not really difficult, but it is slow and tedious. (I KNOW this is all true, because when I finished the last one, I realized I had not gotten my beds level and did every last one of them over.) If I were you, I would use the largest brick/blocks you can manage, because the more and smaller the pieces you are working with the more complicated it will be to get it all level. Plus, I would assume you will have to use mortar with bricks, which means more chances for foul ups.

Once I got the hang of it, I could lay the brick for one bed (8'x3.5') in about two hours. I learned that it's easiest to start at the lowest point in the ground. Get the first one level and then go from there, working across the lowest long side. I used a hand-trowel for all the digging (after I had tilled the entire area) and threw the dirt I removed into the bed. My beds are on a slope, so there were times that after I had dug into the hillside for awhile, I then leveled the dirt with the top of a block and started a new row up from there. It made a stair step effect up the slope. As it turned out, most of my beds are three blocks high on the front and one block high on the back of the bed. It took this many blocks per bed: perimeter of the bed x 2 divided by the length of the block.

I tell you all this to say that raised beds built with bricks will be beautiful and permanent. They will also be more expensive and time-consuming to install. I'm glad I did it. I am also glad I am done! :)

I have not had my first spring yet, but I do expect the blocks to warm the soil earlier. It's also true that the soil in any kind of raised beds warms earlier, but that doesn't mean you don't have to cover your plants from late frosts, etc.

I like your idea of a brick seat.

You can make your own bricks out of portland cement, the smoother cement used in molds for statues with no gravel in it, make molds out of shoe boxes or what ever, then plant them.

If you want to get creative, use ferro crete methods of making a thin short wall. Take chicken wire, put layers of concrete in it a one or a few inches thick while it's laying flat, then when it's dry, pull it up, stack it in the dirt in pieces or one piece depending on how big of a piece you make. It should be inexpensive, but I couldn't tell you the price on a bag of cement and how far it will go, about 9.00 dollars or less. Don't know about the chicken wire.

If you want some really pretty walls, use the portland cement as stucco with stencils, making a raised stenciled design on your garden wall. It will definitely warm quicker, but so will adding lime rocks around your plants, putting a sheet of thin cloth tarp over your vegetables on stakes will heat them up a little too for winter and cool them down in summer.

A lot of the newer gardens I'm seeing are just stacking dirt, no bricks or wall fixings, so your beds don't have to be permanent.

I'm going the other route next year to preserve water and cool the dirt off enough to grow lettuce, cabbage, and peas, by sinking the beds like waffle gardens.