The early breakfast success could be because of what's called a liver dump - your body dumps glucose into your blood ready for the day. I too find that if I leave breakfast my blood sugar goes up, and this is quite a common phenonomen. Some people also find that a supper time snack can help their blood sugars remain more stable, as can eating smaller more frequent meals.
Please don't think anything you did led to the GD. Some women just get it as it can be related to the pregnancy hormones and their effect on insulin resistance.
In the Pregnancy section here, I did post a brief list of what I ate during pregnancy, but I'm a Type 1 on insulin so im not sure if it would suit you. I think that limiting your carbs - that is, not having an excess of them - is sensible. I ate approximately 180-200g of carbs per day in pregnancy. I read a study that suggested 100g per day was the minimum that someone should have during pregnancy, and I would never drastically reduce my carbs to low levels during pregnancy.
'Good' carbs vary from person to,person, depending on their response. As you say, you can use fat to slow down the absorption of glucose eg by adding nuts to your cereal. I ate a 'fatty' low sugar granola mixed with All Bran and seeds for breakfast with full fat milk. Pulses are usually good - lentils, chickpeas, butter beans, etc. Also, you may find the kind of rice you choose can help. Basmati rice has a lower GI so is generally absorbed more slowly. Some fruit will push your blood sugar up quickly, but things like berries are usually ok, especially if you have them with fat eg Greek yoghurt or similar.
If you keep testing, hopefully you'll find a selection of 'safe' meals that you can rotate. But don't panic if your blood sugar gradually rises. Insulin resistance increases as pregnancy progresses and not because you did anything wrong. If you can count carbs, you can perhaps choose/find a good level for,you and baby