Whatever you buy, it would be a good idea to get something with a view to using it later as you progress. So I'd get, in order:

5m wave sail with mast -- This will be your light wind option now, but your high wind option later when you get better at it. A wave sail will be a lot more durable than a freeride sail.

Harness and harness lines -- Not really that expensive, but this will transform your sailing.

110-120 litre board -- I wouldn't go much lower in volume than this, considering your experience level, and this board will become your light wind board later on.

6.3 or so sail -- If you do your homework properly you will be able to fit the 5m and the 6.3 on the one mast (probably a 430).

Once you've mastered going flat out on the 120 litre board and the 6.3, then it's time to get a smaller board, but this is at least 6 months down the track. By then you'll have a better idea of what sort of sailing you like (freeride, speed, freestyle, wave) so you'd get a specialised low volume board to match what you like.

All the gear listed above will still get used as you get better.

How wide is the 200 litre board that you have at the moment? If it's a narrow older board and you're managing to wobble around with a fabric 3.5m sail on a fibreglass mast you'd probably be okay on a smaller board (100-110lt) with a newer rig (carbonfibre is soo much lighter!).

BUT.. you will make things much easier for yourself, and progress much faster by doing like thewindmap suggests and making your graduation a bit less of an extreme jump. I am around the same weight, and had a 152 litre board first up, but found that a 120 litre suited me better to progress.. Since then, I've used a 155 litre Go, a 230 litre Start, and a bunch of smaller stuff too (76, 85, 94, 104 litre).

If you sail somewhere where there's a decent amount of breeze, you could do a lot worse than a Starboard Go 155 or there abouts. They are stable, floaty, and really good to progress on, not to mention heaps lighter than the big old boards. The hull shape means they track up wind very well in the light stuff without needing a centreboard, and still perform comfortably in 25 knots.

But.. if you're fit, energetic, and a fast learner, on a tight budget I'd be inclined to look for something in the 120-130 litre range as that will last you for quite a while as a free ride board without being too much hard work as you get used to it.

It's probably best to describe where you plan to sail, and what the conditions are usually like so that you can get more specific advice.

cheers 4 the advice with the board ive got should i try using a 5.7 m sail on it which is in the shed in reply to questions sail in mandurah wa open ocean and an estury close by (waist deep) mainly 15 to 20kn thur summer looking to buy second hand and don,t mind older stuff its works well not sure what type of windsurfing probaly freeriding budget not to big