Hello and welcome to the forum. Traditionally working food was formulated with extra calories from a higher fat/protein content. However, nowadays there is little or no difference between that and ordinary dog food because there are some high quality extruded foods that exceed the protein levels in some of those classed as for working dogs.
Food that has the working label is exempt from VAT so if you go for those it is possible to save money. Sometimes they come in plainer packaging.
There are no cold pressed foods in the working category. They are usually generic ie for all life stage. Of the ones sold by UK companies, Gentle has a protein level of 29.1%, Guru 27.8%. Cobbydog is made in the UK and has 37.1%. Gentle and Guru attract a slightly higher nutritional score. Tribal may be worth looking at too but there are others, as you have seen in the dedicated thread.
As your dog needs to muscle up and will be getting a fair bit of exercise when grown, a higher protein level should help to achieve this. There are plenty of high quality extruded foods that have a high protein content. You need to decide whether you want to feed extruded or cold pressed food and there is information on here which can help you decide. Cold pressed food has the advantage of not being exposed to the high temperatures of extruded kibble. Also, it is said to be easier to digest.
If you go for cold pressed food, Gentle and Guru attract a slightly higher score than Cobbydog but any of those foods would be good. You would need to contact the company re the RDA as your dog is young and needs to gain muscle.
There are some benefits to enhancing dog food by sometimes adding suitable fresh cooked ingredients because it gives variety. Vegetables need to be cooked and mashed to assist with digestion. Fruit such as blueberries can be given, as can chicken, white fish, sardines, scrambled eggs etc. In the past I have found this works well with cold pressed food.
Regarding delivery charges, with Zooplus and Bitiba it is free with a spend of £35. Don’t worry about the maize - I am told that it is only the maize germ that is used and this has nutritional benefits. For Amazon Prime members it would be useful to have a variety of CP foods sold on there as it would save on delivery charges.