You are lucky not to have back hair!
I am not a big fan of shaving with the grain when using a blade. That does not shave close enough. You would be better off using an electric if you have a major problem with ingrown hairs. A good electric will beat a blade shaving with the grain every time. The best electric I have found is the Braun Synchro. The 7526 is self-cleaning and is $129 at Wal-Mart. The 7505 is about $109.00 They stand up well to body shaving and have a two-year warranty. It is a dry shaver only but it shaves better than the best wet-dry, which is the Panasonic Linear. The Panasonic linear is a good wet shaver but does not work well on coarse hair like beards. Also the screen on the one I tried failed after about two weeks. A Braun screen (foil) will last about 6 months with body shaving, maybe even longer. The Panasonic I tried was the $299 (now $249) model from Sarper Image but still the Braun was better. Stay away from rotary shavers. They are not as close and are much slower in getting the job done. Pre-shave cannot be used with the Braun but it is not necessary. As long as your skin is clean and dry the Braun will work fine.
Stay away from the cheap disposables! That could have been the reason you had so much irritation shaving against the grain. No blade I have tried compares to the Mach 3 Turbo except the original Mach 3 and the Venus 3 which were (are) still pretty good. The Venus 3 women’s shaver is very good and may be preferable for shaving in the shower as it is easy to grip and the handle is designed for body shaving. Don’t laugh, lots of guys use the Venus 3, at least vefore the Turbo came out. The Turbo, the ads say is meant for shaving against the grain.
When I first shaved my chest I broke out and had quite a few ingrown hairs too. I switched to the Braun (older model 5525) at the time and it gave acceptable results. I eventually went back to a blade at least before I would go to the beach or out in the boat. After using the combination of an electric almost every day and using the blade a few times a week my skin adapted to it. After that I had much less problem shaving. If I had used a blade exclusively my skin may have adapted faster.
I have a few suggestions for blade shaving. First, upgrade to at least a Mach 3, preferably the Turbo version. If you shave in the shower get some Suave Moisturizing Body Wash (white bottle) and put it on and lather it up. Get some Edge Pro Gel Tough Beard formula and put some on top of the Suave but don’t overdo it or the razor will clog. If it clogs the blades of the Mach 3s clean very easily under running water. Shave against the grain. I never tried a Mach 3 with the grain although it should be much. much better than a Bic.
BTW Gilette recommends that men suffering from ingrown hairs shave every day and that may help too. When I used and electric and before I went under the laser, I had so much chest hair I had to shave every day.
After shaving apply Tend Skin. It really helps prevent and treat ingrown hairs! I treat ingrown hairs by lifting them up with a sterilized needle and yanking them out with tweezers. My method has always worked and never made the problem worse as some may claim. If you have any really bad ingrown hairs, give the Tend Skin a chance to do its thing, even it it takes a couple of weeks (in extreme cases).
I am going to try some Moore’s Unique Hydroglide Shaving Gel if I can find it. It’s supposed to be really good. Since I haven’t had my legs lasered yet I will try it there and report the results.
Sorry for the long post but it had to be this long to cover the topic.
Hope this helps.