I soaked again and put another poultice on, there is a definite slit at the top of his heel bulb, but nothing coming out.
And therein lies the issue.... The reason abscesses evidence with severe lameness is not so much due to the fact that there's infection; instead, it's because the infection is "walled off"... it's basically pressurized.
Once the abscess vents, the pressure is released, but the infection is not automatically resolved. This is especially true when the abscess vents at the top.... primarily because it's hard for things to drain uphill.
Along with the uphill drainage problem, there's also the problem of time... A top vent is usually natural while a bottom vent is usually man-made.
While the general horse-owning populace currently has a tremendous affinity for all things natural, it's not the best in this case. It allows the infection to meander around rather than taking a straight path, and it tends to drag on forever, allowing the ick to thicken and establish itself as a thick, sticky goo.
So... your horse has relief, because the abscess vented, but the situation is not likely resolved. You indicate that the area around the bulbs is looking white. That likely means the hoof is overly hydrated (probably was to begin with from the environment, and that was exacerbated by all the soaking and wrapping). Start drying the hoof capsule! Use topicals (Keratex hoof hardener, Venice Turpentine, pure gum spirits of turpentine, Hawthorne's Hoof Freeze, Crossapol, Betadine, Zenadine, a blow dryer, or whatever).
Get a syringe and inject good (but mild) stuff into the opening—some sort of tamed iodine—betadine or zenadine—is probably best. Leave the area open when the horse is in a dry, clean environment. Try to protect it and cover it for turnout.
A boot is probably not the best option for turnout, as it will tend to trap and promote moisture. Instead, seal the opening off with something productive that will adhere and hold. Hawthorne’s Sole Pack works well for this; it will go on kinda like Playdough, and it will usually be sticky enough to stay in place. Another option is to use a small piece of Animal Lintex, held in place with some good tape (think Elasticon, not Duct).
Hope this helps!