I had the same attitude of 'being able to afford and expecting to lose' when I started trading, and as throwing myself in the deep end as you say had always worked before had no reason to believe this would be any different.
Whether you decide demo trading is for you (it wasn't for me) or whether you need something small at stake to focus your learning, however you go about it, just think about the logic of losing what you can 'afford' - in truth, if you are making this a long term commitment, then you have no idea what you can afford, because you have no idea when that point of being profitable will arrive. And just because you 'expect' to lose doesn't give you any expectation of how much you can lose in relation to what you will learn.
You can learn trading by paying as much as you like. Why pay more? Surely you wouldn't pay more than you had to for anything else in life, especially for something which you have no idea at what point it will start providing a return. For every 100£ loss, that could have been 10 separate lessons, 10 separate trades, or even 20, 30... You expect to lose, so lose small and learn lots. Unless its the thrill that gets you, in which case that's a whole different matter.
A friend of mine who is trading and used to sell exotic holidays put it this way: It is like offering someone a holiday where they could buy it for peanuts, but instead they choose to pay him handsomely for it because they can 'afford' to, and keep paying, but they have no idea when or if they will ever get the opportunity to pack their bags and enjoy it.
Anyways, just my tuppence...