If you’re paying for oil deliveries compare the price to Forbes Fuel or one of the other companies that are known to be cheaper. I don’t know how your landlord can make you use Standard. Landlord probably contracts with them for furnace servicing but too bad

Also look into Eversource weatherization program. I’ve never used it but I hear renters can use it and it might be free. I hear they can add insulation and seal things up. It’s part of a state mandated program