The stone should mitigate the freezing. It would heat in the sun and give off heat at night. I know some old time greenhouses were built against a brick or stone wall so it would help keep the plants from freezing at night.

Of course this is just theory as I have never tried it.

I used to have a triangular raised bed edged with stone. The south/SW edge was the raised section since the bed was built on a slight slope. The other two sides were edged by brick walkways and bricks. Along the rock edge I had a couple of different thymes. One creeping variety overflowed on the walkway and despite the shallow root system did fine here in NH. But the quality of my soil and the amount of sun was not as good as I have now. You might find a 4x3' bed is too small if you have full sun. When we first moved to our present house I made an herb bed along a walkway but it probably only got 4 hours of sun. Things did fine but after renovations were done I moved the culinary herbs to a bed around our small kitchen porch. Each small clump became huge clumps in a single season. My sage is probably about 3' in diameter. The tri-color sage isn't reliably hardy here so it has stayed small.

I live in Northern most Central PA and use raised beds for everything from flowers to veggies. The soil here is a mix of clay and rock. After the first snow has flown, I cover my raised beds with a layer of loose mulch (dead leaves, newspaper, straw, bark whatever is handy) and then I cover them with a layer of landscaping fabric and tuck it all around so that they are a nicely wrapped presents. When the sap starts running in the spring I unwrap my presents.