I wouldn't necessarily choose a low fat diet, often low fat foods are filled with sugar and additives to make them tastier.
I am trying to choose a diet that is full of natural unprocessed foods - lean meat, fish, eggs, lots of veggies and fruit, natural yoghurt, raw nuts and seeds, with wholemeal bread, some cheese...
...and the occasional treat like frozen yoghurt or icecream or slice of fruitcake.
Lots of water and herbal tea and 2 cups of english breakfast tea a day as well.
Am avoiding: crisps, fizzy drinks, salted nuts, white bread, pastries, croissants, sweets, that sort of thing, although if I have a mad craving for it, I might have one once a week. I do think the more you have of that stuff the more you crave it, whereas it is quite hard to O/D or binge-eat on cooked chicken or satsumas or carrots dipped in hummus or guacamole.
I was BMI 25 when I got pregnant having slimmed down from BMI 29. For the first three months I could only eat nursery food like marmite soldiers and boiled egg and really bland stuff.
Good luck and try not to worry too much, if you are worried talk to your midwife.