I don't think disregarding people's help and showing off a poor attitude towards fishkeeping will help your betta get better.
Everybody here has given you a "straight up answer":
1. Get a heater, it is more important to the health and livelihood of your fish than a filter
2. Do the weekly water changes; I remember Bobo was a little pouty when I did water changes for the first time, but now he is used to it. However, if your fish is/are CONSTANTLY being super stressed out (i.e. sitting at the bottom for several hours after water change) you might be either putting in freezing water or not enough conditioner. Just do a 50% water change on a Saturday, then you can monitor their behaviour on Sunday before you have to go to school/work/whatever.
Sorry for being blunt and very direct, but panic seems to have a hold on you, we're all here to help.