I think what you're doing sounds fair to me. We have a slightly more casual arrangement, mostly because we've never been strict about finances and we've so far been too lazy to set up a joint account. But I would say ultimately it works roughly the same as your arrangement, except I don't actually know how much disposable income we each have at the end of the month and if one of us needs more, the other just hands it over.
We each have our bills we pay monthly and then there are a few less regular ones we split when we need to pay them. Dh pays the rent and a few other things, like internet, etc. He also tends to pay for more leisure activities as a family (like meals out, days out, etc.). I have always paid for nursery and food shopping and clothes, etc. for our dd. Until recently, that worked out to be roughly the same each month. Our dd is now in school though so no nursery bill, but I'm also starting mat leave, so my salary is halving. So still works out roughly the same. He is paying more but making more and I'm paying less in bills, but earning less for the next year. We don't have it worked out to the last quid though. Things like council tax, heating oil, etc. which are big periodic expenses, one of us pays it and then the other transfers over half, give or take.
I suspect with this arrangement I end up paying out more of my actual income and have less disposable left over as I tend to pick up more day to day expenses, which probably add up. But it really doesn't matter because if I ever get low, my dh just transfers a bit over until the end of the month. Similarly, he's self employed, so his income varies seasonally. In the winter, he earns less than in the summer, so if he needs more, I transfer some over to him. There is no such thing as 'his' money and 'my' money, strictly speaking, though we have separate accounts. Neither of us goes without as the other would just send a bit of money until the end of the month (obviously, with no expectation that we'd get it back).
When we first met, we were both students and money was very tight, so we've always just looked out for the other. Money isn't tight now and we have enough to live comfortably on, so it's no big deal. I'd feel differently though if he was running out of money every month because he was spending it on something stupid. But generally we're pretty sensible about it, so it's not a big deal. I don't really see (unless one partner is really financially irresponsible, has a gambling problem, etc.) keeping money totally separate or having a 'mine' and 'your' mentality with money. I wouldn't want to see my partner struggle when I could spare a bit of my disposable income to help them be a bit more comfortable. Realistically, any money either of you earns is made possible by the other, so it seems silly to be selfish about it. My dh started a successful business because I made financial sacrifices and did all the childcare when he was starting out, and I have a good job and a good career because he's picked up and done the school runs and bedtimes and weekends when I've been working away, etc.