OP - I had a similar situation before we were married. DP earned a lot more than me, we had (and still have) separate bank accounts into which our salaries went. But then I had a big lump sum as a deposit (from inheritance) and he didnt. When we bought a house, we talked to the solicitor about putting the house in joint names but with differing % assigned to each. It ended up being something like I owned 65% initially, but tapered off as he paid more of the mortgage than I did and so after x years it would be 50:50. As it turned out, we got married a year later and had kids and I am a SAHM so it's all void now.
Since you are not married, you DO need to consider your own future financial wellbeing. It makes perfect sense for your DP to have good pension provision, as it means you wont have to support him! But to give him 50% of house ownership means that in the case of a split, you wont have anything to fall back on and he ends up with half the house AND all his savings. That's not fair whichever way round the genders go. The fact that he CAN (and does) work now but its just more convenient not to, means that he does have it to fall back on. In the case of many SAHM/SAHD, they have left their career and find it very hard to break back into it a few years down the line.
TBH your relationship sounds like mine (other way round though). We chose for me to give up work when we had kids. DH's job (weird shifts, working away) makes it very very difficult for me to commit to most types of work, and I am very happy to be a SAHM, and I admit I have a pretty easy life! I do tiny bits of freelance stuff and keep all the money I earn. In addition, DH puts money in my account every month; as you said, for things I want to buy but not have to account for. We have a joint account and credit card, funded by him, for household/kids/hols but we are both accountable for this. He has his own account too, I have no idea how much is in it, and I dont need to know. We want for nothing, and he would never refuse a big purchase if it's important. ie we actually TALK about big-ticket expenditure!! Neither of us would dream of paying more than £100 for anything from the joint account without a little consultation with the other. And it has nothing to do with who earns more or whether it is a SAHD or a SAHM.
It's a shame that to have to be married to automatically get the sort of rights that ought to be available to everyone. But until this changes, you do need to look at the future and make sure you, he, and your children are protected in the event of a break-up.
You will find your conveyancing soliciter should be able to help you on the wording on your ownership paperwork. But please ensure you and DP are straight about all of this before commencing! Good luck 