Light reading on peat and compost...
http://perrysperennials.info/articles/peatcom.html
You will need some aeration for the soil, like perlite... Amazon doesnt deliver to you?
Not knowing your existing soil, but knowing you want to add compost and peat, you should add some Dolomite Lime to help balance the soil out... any chance you can get a soil test kit? Also from Amazon? Or a local source?
Remember, the soil is the life line to the plant. The better the balance and mix, the healthier it will be. Will it get to the point of harvest without a good mix, quite possibly, but it can cause issues along the way without a good soil, or it could kill it. Think about the soil being your heart, it does better when cared for and you are stronger with a healthy heart.
Overall the plant does not look in that bad of shape, although when going to flower, the stresses it has been going through will impact it more so if not corrected. If you can grow good tomatoes, you can grow cannabis. Everyone goes through trails and errors with cannabis, don't over think it too much, but you have to remember the basics it you want a good result.. good soil, good temps/humidity, good light, decent air/circulation, nutes/water when needed and the plant will tell you this. To many times people add an odd balance of nutes and cause the issues.