Sometimes customizing is necessary because of an injury or the inability to do, for a short or long period, the kind of exercise you formerly did. When you're used to customizing for fun, doing it under duress won't seem like such an imposition. Either way, experiment until you find activities that make you happy as well as healthy. Choose your exercise using the same criteria you'd apply to choosing a date--that is, attractive to you and able to hold your interest for an hour.
Happiness comes from accepting the present situation, whether it is something you wish to savor as long as possible or change as quickly as you can. Neither is possible without acceptance as the starting point, because without acceptance you are living on the periphery of your life. There at the edges, you can't fully enjoy the good stuff or do anything about the rest.
Life has its rhythm and we have ours. They're designed to coexist in harmony, so that when we do what is ours to do and otherwise let life be, we garner acceptance and serenity.