Seconding the mhohner link, you must have a read through that. And hoffy's body recommendations are good; I would start with a 5 since they're like $10 and support
everything, then think about a 7 or 9 depending on your desires for speed/functionality or indestructibility.
Your problem however is that most of the lenses you own are APS-C and will not completely cover a film frame. You need "full frame" lenses for use on film, otherwise you get a black outer circular area on the image. I think the 75-300 is your only full-frame lens.
Because you don't really have any investment in film-compatible Alpha lenses and because I am biased*, IMHO there is not a lot of point shooting 35mm film anymore because digital has finally gotten notably better. Medium format is a different story and you can make incredibly good photographs with cheap old medium format cameras. Have a google for Mamiya and Yashica TLRs (
examples), then also read up on Mamiya/Pentax 645 systems and RB67/RZ67 (
examples).
Just be aware of the non-obvious options and don't let the tail wag the dog in terms of your existing equipment. Not all of my above suggestions are for everybody by any stretch of the imagination. See if you can find a local camera club and borrow a medium format camera or two. A 645 SLR or 6x6 TLR can be lighter and smaller than a DSLR with grip, a 6x7 has 4x the film area of 35mm; the only drawback is they eat 4x as much film so you learn to slow down a bit
* I shoot a Sony A99, Mamiya RZ67 and Toyo 45A.