Hi Gromby,
I agree with the Free Flight option if you are going to buy a new board, the dimensions will work well for you and at least it is a quality board and not PRC rubbish.
If you are happy to go second hand then I reckon look for an 80's or 90's era Mini Mal. Plenty of older ones about still and most are around the 8'0 to 8'6" length.
I'd go for one with at least 22" or wider for better stability under foot and don't be put off by a single fin option, a bit stiffer to turn won't hurt you while you are learning before moving on to a twin, thruster or quad option.