I don't know where some of these ideas come from. Yeast becomes dormant at temperatures above that found in a refrigerator. In fact, when making sour dough starter and keeping it without constant attention, it is put into the fridge to cause it to go dormant.
Allow your starter to come to room temp. In 24 hours you'll see the frothiness you expected. (Onlly 1/2 tsp of yeast for 3 cups of flour is a little on the minimal side, but after a day of growing, it should suffice.)
I've noticed a number of recipes that call for slow rising in cool places. As the process is identical whether at cool or warm temps, I cannot understand how it can make a difference. Flavor and testure will remain the same either way.
Emm, I've been having excellent results by warming my oven for about one minute, then turning it off and opening the door to let the very hot air out. Then I put the dough in the oven to rise. At the slightlly eleveated temp - around 100 F, it rises rapidly and reaches its maximum in less than an hour usuually. Then I punch it down and repeat. Works for me. Maybe it wilol for you, too.