Hi Edge,
The ideal board size for most conditions is your weight + 20 kg's. This allows you to uphaul in low winds, while still being small enough not to act like a barge in higher winds. If you're 65 kilos then I'd look at getting an 85 litre board. Still, you can learn to waterstart and get to the straps on a 120 litre board. Tacking and gybing with so much flotation should be a piece of cake

I would suggest that you learn to waterstart before venturing out into waves however, uphauling with swell rolling past is difficult to say the least (been there, tried that, got spanked big time)!
My experience is as follows:
Bought a big old 180 litre 'plastic fantastic', probably over 20 years old, learnt to get going, tack and gybe on it. After a while it got a bit boring so I bought a board that was my weight (85 kilos) + 20 = 105 litres. This board allowed me to learn how to plane, waterstart, get into the straps, gybe, chop hop, and now I'm going out into the waves every now and again, as well as getting close to carve gybing.
If I were you I'd aim for something around 85 litres, this will feel like a matchstick compared to your old board but after a while you'll get used to it, and will wonder how you ever managed on your old Tiga.
Don't worry about carve gybes yet, they are fiendishly difficult especially if you're not in the straps yet. Try slowing down, grabbing the uphaul rope, holding the mast to the outside of the turn, and slowly walking around the mast as the board turns under your feet, then grabbing the new side of the boom once the board is pointing in the right direction. At least this way you get to stay upright

Once you've got that then try a slow 'flare gybe', sailing out clew first then flipping the rig. So many skills to be learnt, and so many moments of pure joy when you learn a new skill.
Enjoy