I think my ball python is bored

[JoshSloane]

28gal is a bit small for an adult ball python, even a male one, if you want to give him a nice and enjoyable time with you. As a rule of thumb, the length of the tank should be long enough so your snake can completely stretch out along the side of it, and I've read a couple times that 40gal is the minimum for a permanent adult home, better 50+ if you have the space. (note: the bigger the tank, the more hides you need, and the more things to clutter it up and reduce scary open space)

Completely redecorating might put him off feed, but you probably have better experience with your own pet there and can judge that better than me!
Enrichment mainly consists out of providing as many hides as possible, lots of cover like big plants, things to crawl over and under, perhaps even a second level as males have been found to enjoy climbing to a certain point! Also a second level increases the "accessible" ground space in a tank.
You can also try mixing up the substrate, you could make a 70/30 mix with a different type, or put one half in that substrate and the other half in a different one, whatever, either way some pet owners have reported that their BPs seem to be interested in the change and enjoy exploring it. If you have enough hides and objects, you can also try swapping them up once a week or so! Taking one object out to replace it with another and slowly cycling, that way there's always something new to explore without stressing them like drastic changes might do!

So yea, enrichment is mainly to have a big enough space for them, and to give them options to choose from on their leisure, like where to lie and where to sleep, so they're not stuck with only one or two hides they MUST use.

EDIT: I've mainly gathered this advise from ball python pet owners over the past year in preparation, so these standards are for pet animals, which (in my opinion sadly) are seldomly met by breeding animals.
I understand fully that it is impossible to hold up pet standards if you have God knows how many animals for the sake of breeding, but if you only have one --- why not provide more than the bare living minimum? Go nuts, if you have the funds and time, grant them a nice and enjoyable snek life!

The 'rule of thumb' that you state here is not correct at all. Please be more careful in the future to not disseminate information online as 'rules' when they arent correct. There is not a single snake that needs an enclosure that can accommodate the entire length of the animal. Measuring the capacity of a tank for a snake by the gallon is useless, as BPs are primarily terrestrial, and floor space is a better indicator of the appropriateness of an enclosure. The general consensus is that most adult BPs can live comfortably in approximately the dimensions of a 41 qt sterilite tub (34 7/8 x 16 5/8 x 6 1/8). A better approximation to the utility of a cage is that when the snake is in a full coil, you want to have about the area of 4 coils available for space as a rough estimate.

Snakes do not need enrichment. They are primordial animals with a very basic brain structure. Coming out of of the enclosure once in a while for some exercise is great, but dont feel bad if they arent handled every day.

I got through multiple graduate degree programs while owning dozens of reptiles, im sure your BP will be just fine.