All my soil is lovely claggy clay with a huge amount of pebbles from tiny to fist sized. It bakes hard as rock in the sun and is terrible in the wet. The amount of stones means it's impossible to even put a fork in, let alone a spade! Clay soil is actually very good once you doctor it. It is an ideal 'base' to mix with compost to form a very good soil mix which holds moisture and actually saves on watering. I constructed my own sieve using 2x2 batons and 1/2" chicken wire, it's sized to fit on top of the wheelbarrow. When I mix up some soil, I use about 50% compost, 30% of my clay soil and 20% sharp sand. If you want organic, use rock dust to re mineralise the soil or chicken manure pellets or seaweed etc, if you want to use fertilizer can't go far wrong with growmore.
I have solid clay clods that are unworkable about 12-14" underneath the topsoil, what I tend to do is either dig it out, or loosen it up then mix in a load of manure, and hopefully the worms do the hard work then.
If you can't be bothered sifting etc, you can buy topsoil in bags from b&Q or homebase etc. I'd mix it about 50/50 with compost and add whichever fertiliser you decide on. It's up to you, good luck.