Commercial Lease Negotiation

I am planning to rent a tiny office space in West London and I am seeking someone to provide legal advice during my negotiations with a landlord.

I've already made an offer and the main terms were agreed with the landlord (lease term: 3 years, 2 months deposit , break clause - after 2 years).

Basically I will probably need to review the lease agreement provided by the landlord or draft it together with the landlord's solicitor with the provided the Head of terms (property agent wasn't clear about this)

Also I want to make some improvements to the property at my expense but don't want the landlord to increase the price after 3 years due to these improvements made by me.

I'm quite literate in legal terms and I'm not willing to pay huge money to someone who will tell me common sense and explain me what break clause means.