I have been thinking about getting a SUP and have no idea where to start, so hoping someone might be able to help in the sort of board I might need to look at - there appears to be a vast difference

I am 6ft, weigh about 85kg and surf regularly. Generally it would be used most in flat conditions but would probably take it out on small days as well.

any "helpful" advise would be appriciated!

For your height/weight/needs I would suggest perhaps a Naish 9.5 Mana or a
Starboard 9.8 Element. Both boards are very stable/good paddlers and surf unreal. The Naish is a little more stable in open water and an easier board to surf when you are just starting out sup surfing but the Starboard is a slightly better paddler (faster). Price wise they are fairly compatable but you can get the Naish in AST construction (very similar to the starboards) for quite a bit less than the Starboard.
Both boards are awesome, fun boards and you and the family would not be disappointed by either board.

I recomend the new AST 11'4" Naish Nalu.. great price.. great board.. and IMO perfect for what you want.

DJ

Ok - cheers

Am 82 kg, and 6' also, never surfed but kitesurf and paddle outrigger canoes, started with a 10' Naish AST Mana. Found it an easy board to start on but it's more wave specific and not much fun to paddle in flat water. Was disappointed in the soft finish of the AST, which chips and marks very easily, but is an lighter and easier board to lift onto cars.
Have switched to the Naish 11.4" Nalu bamboo construction which I love, am slowly catching waves and enjoy riding it in the flat water also. Being thinner at 30" getting my balance has been a workout as I learn to move my feet and it's a lot harder to turn quickly to catch a wave, but I feel with practise with last me a while and I'll grow into as I improve. The quality and finish is superb and not much more than the AST, also coming with a bag.
Good luck!

for mostly flat water I recommend something between 11' and 12'6. Thats long enough to be a good paddler but not too long you cant take it in the surf.

I started on a PSH 10'6 wide allrounder and love it. Paddles fine in flat water and surfs great in all conditions. I am on a 9'3 know but still love to paddle the 10'6.
p.s. I am about 86kgs

I started on a Starboard 10'5 Drive as an all rounder with the intention of my wife (65kg) using it for flatwater and me (105kg) in the surf with a little flat water cruising.

This has been a great board for us but with a bit of experience now and having tested quite a few boards I'd haye to say for what you want to do my choices would be between the Coreban 11'6 Cruiser or Angulo 11'11 Big Buggah. Both are great flat water paddlers plenty stable but you can still have a ton of fun in the surf.

Good Luck!!