Forget the peat, its environmentally unsound to use it. John Innes potting compost, whether it be 1, 2 or 3, is wasted on the ground, its meant to be used for potting plants, and its price reflects that.

If you want to improve the texture of the soil in your border, and feed the plants better naturally, and increase the humus levels, use Garden Compost. You can buy it at the garden centre, sold as Garden Compost or sometimes Soil Conditioning Compost. Another useful thing to use is composted animal manure, which they also sell in bags. Either, or both, would be good.

If your soil is heavy clay, adding sand and gypsum or lime (depending on the pH of your soil) to the mix would help even more. Compost is usually a safe bet, though.