So taking some of your suggestions and suggestions of the Pet Mart clerk I added 1 black mystery snail and 2 ghost shrimps in with my betta (2.5 gallon). Here's what happened:
During the first two weeks life was all good and everybody got along well, the betta would rarely notice the ghost shrimp and would occasionally swim up to the snail and give a long look before swimming away. Then one night as I was feeding betta, one of the two ghost shrimp simply swam up and clamped on to betta's tail causing betta to go crazy swimming all over the place while dragging the shrimp behind him; the ghost shrimp quickly swam up and stole some of the bloodworms and went back down; betta finished his meal and went right back for the ghost shrimp; sensing it was going to be a long night for both and not wanting to cause any agony to my betta i took out the ghost shrimp in a separate container but before i could take out the second one, the first one died (i'm guessing water temperature change) so i kept the second one in..
a week later i came home and noticed that the second ghost shrimp was dead and its body was trapped between a few marbles in the bowl; im not sure if betta forcefully trapped her or it got stuck on its own; either way i thought id comeback in a few minutes and clean up the tank and all i see is betta viciously feeding on the ghost shrimp; im guessing he enjoyed that dinner..
a couple of days ago the mystery snail died and i threw her out, not before she stunk up the water which had a terrible smell..
my suggestions: ghost shrimp were great and fun although hard to locate sometimes. its fun watching them trying to avoid the betta. they're cheap so can be replaced and they didnt produce much of a mess.
on the other hand although it lived long, i think the snail is a terrible tank mate; it stayed inside of its shell almost always. was very boring. made alot of mess and had a bad smell.
hope this helps in your future selection of tank mates for bettas in small bowls that don't have a filter.