https://apply.oxfordsu.org/colleges/suggester/ the info on this tool is a bit out of date so please do double check with the college's websites (usually if you look for the JCR website that will have more up to date info on this sort of thing) but it might give you an idea of some initial colleges to look into further.
In terms of financial support the main thing you would get aside from student finance (assuming you are a Home fee status student) would be centralised university bursaries - Oxford Bursary and Crankstart are based on Student Finance's assessment of your household income. There are also other scholarships you can look into but you usually have to meet quite specific criteria. Financial support is less affected by college - colleges do have different levels of financial support for things like textbooks and study supplies, but its a difference of a few hundred pounds maximum. The main support you would get on top of student finance would be from the uni not your college. Though do check if there are any college specific scholarships as they occasionally pop up. There's a search tool on the Oxford uni website for scholarships.
also to give details on my college (Corpus Christi) - First years are guaranteed college owned accommodation usually across the road from the main site and you can request en-suite if you have a specific requirement (I think religious requirement would be acceptable!). However the first year ensuite rooms don't have good access to kitchens, its usually just a microwave/fridge freezer/toaster/kettle situation, though I believe they are looking into improving this and also might be becoming more open about letting you bring some types of portable cooking equipment if its PAT tested, but I wouldn't rely on that if kitchen access would be important to you. The college hall kitchen are also pretty good at working to dietary requirements like halal, and Corpus hall food is generally good and pretty cheap. In second year most people live in college-owned accomodation that is about 15-20 min away from college, and there are options with both ensuites and kitchens. In final years people move back to college (where again you could have an ensuite, but may not also be able to have full kitchen access) or stay in the previously mentioned accommodation that is a little further away. In terms of college-specific financial support you can claim up to around £150 per year for academic expenses. There are also £200 scholarship awards for people who do well in their first year exams. There are also lots of random funds for things like items for hobbies, travel, music etc. And if you get into financial trouble there is a possibility to access hardship funding as well. I am graduating though so this information may not be totally up to date by the time you apply!
I'd suggest drawing up a shortlist based on research with the college suggester and JCR websites, and then come visit on an open day if you can (you can get need based travel funding and accommodation for these if you qualify for it and apply for it well in advance) to check out what it is like.
As others have mentioned you may not get accepted to the college you apply to and end up somewhere else, but I'd imagine most colleges in Oxford will have the ability to meet your needs if you communicate them when you've been offered a place so don't worry.