Next steps advice for raising roof for loft conversion.

Hi - Long story short, we have a 3 (more like 2.5bedroom) detached house in North Beds and in need of additional space. Our loft is under 2m and therefore cannot be converted as there is not enough height. Had a chat with a loft conversion specialist and he said he can do it provided we get permission to raise the roof height by 1m and check with our council's planning informally.

Now here is the real challenge. I don't know how to go about the next steps. I emailed council's planning and they asked me to council's planning page and asked to submit pre-application advice. I paid fees, asked qns providing photos and they rejected and refunded the fees saying that the form is not for that. They redirected me to Lawful Development Certificates, but reading that section, I'm not sure that is what I need.

I asked this in FB, and a planning consultant said there is only less than 50% chance of approval as my neighbouring houses are more or less same height. Ours is an early 2000 newbuild estate and there are plenty of 3story, loft converted houses, but not in our street.

What do I do here? Do I reach out to a planning consultant? I had a quote with a planning consultant and they quoted me ~2k. Will any planning consultant do or should I look out for someone who's within our council area?