Welcome to the forum!
Hopefully some of our forum mums will be around to share there stories - in the meantime feel free to have a look through other threads in the pregnancy sections ("pregnancy issues" and "small talk") to get an idea of other people's experiences!
I have to say, I have some serious qualms about an endo that says not to carb count and not to adjust during pregnancy. You will see if you read other pregnancy-related threads that it would be pretty much impossible to achieve the kind of tight-range BG targets required in pregnancy without near constant adjusting. Even in a non-pregnant person, if you just ate the same things every day, your BGs would be okay half the time and out of range half the time, because there is so much more to BG control than just food and insulin! In a pregnant woman there are also massive hormone changes to deal with. Plus, just with morning sickness and cravings, I don't think it's humanly possible to eat the same things all the time while pregnant!
Basically what your endo is asking, first of all is impossible, and second of all will not help you achieve good control during pregnancy, in fact quite the opposite. I wonder just how many pregnancies this endo has overseen with this method (can't have been many) and what the outcomes were (can't have been very good) - might be a good question to ask her, actually! Add to that the "it only takes 5 seconds" which suggests a lack of empathy, understanding, and helpfulness when it comes to actually having diabetes in the real world (as opposed to in a textbook or in a hospital!) and I might be in the market for a new endo if I were you. I know they're hard to come by though and you can't always switch up just because you want to. But pregnancy with T1 is enough work without fighting an uphill battle all the way with your medics!
Be aware that even planning in advance, you will still have to go through the "error" part of trial and error. Things don't always go according to plan with diabetes, life, or pregnancy and you will be dealing with all three! However, if you aren't used to carb counting and adjusting your insulin yet, as your endo has steered you away from it, it's a really good idea to get comfortable with it BEFORE you're pregnant and everything goes A over T. If you're not comfortable doing this on your own, there are courses you can take (including online ones) or you might be able to schedule an appointment with, say, a qualified DSN who will be more open to the idea and can show you the ropes. I'm not actually in the UK so someone else will have to give you the info on where to go/who to contact but I know there are resources out there! And of course we will be happy to help in any way we can