I'm also hypo and I found at a younger age (before I knew I was hypo) that a good way to keep the metabolism going is to eat many small meals throughout the day.
Eating six 300-calorie meals in a day is an 1800-calorie diet (what I use). You would need more meals for the normal 2000-calorie diet that is recommended for the average-sized person. Of course, athletes need more calories and sedentary people need less. You should never go below 1200 calories per day, otherwise your metabolism shuts down and goes into "fat-saving" mode because it thinks it is starving, which causes you to gain weight.
The more often you eat, the faster your metabolism is. When your thyroid is under-active, your metabolism slows down, so eating this way will keep your body constantly going and your "engine revved".
Hope that helps