Compost:
For seeds, I buy coir blocks and mix it with anything else from the previous year that was bought in compost as it is less likely to have weed seeds in it.
For potting compost I make my own now. A mix of worm compost, tumbler compost, sieved compost bin compost and leaf mould. Plus I often half fill the bottom of pots with the loam I've now made from the turfs we removed and stacked to rot down.
Last year I didn't have to buy one bag for my plants, I used my own which is pretty good going being that I moved here in November 2021 so had none to start with. I got given one bag of absolute crap in exchange for some tomato plants, which got dried out [it was sopping and stinky] and used in pots. Later inthe year I bought one grow bag to try germinating spinach in, which worked well so I have now used that as my mix with the coir blocks I bought this week for the first batch of seed sowing.
Here in France there is genuinely zero decent compost so if I buy one I will only be buying through a local organic nursery which buys in bulk. It is more expensive but it makes you less careless with it.
In the UK I used to use Fertile Fibre, which was the best and expensive but again, worth it. Or New Horizon. Apart from that I'd stick with using grow bag compost, it does tend to be better quality than just bags of peat free.
There used to be a company who made peat free john innes mixes, which were superb but I'd not seen any for a fair while before I left. After Covid there wasn't any peat free so I had to buy 3 bags of peat stuff and I hated it. Which is basically why I decided to just pitch in, use my own and pull out any weed seedlings that grow from it.