Well, I'm no expert but in recent years I haven't had much problem with seeds. I do use Seed compost and don't mind the price cos I need so little (you don't want it to be "rich", but for the larger veg (toms, cukes, courgettes etc) I use a little electric propagator (kitchen windowsill) that I've had for years. Everything came up quickly this year.
But for the next stage I used Westland Multipurpose (used it for years) and it's taking its time. I even used a bit of tomato food to bring things on but they are still way behind (though look healthy enough.
All is peat free, has been for some years, and it seems to look fine now (after some years of rubbish). I usually aim to get things outside/in the greenhouse by the end of May - which it now is - but most things are still very small.
I am potting up my one cuke into its final pot (doing it in the kitchen cos its tipping down outside!) but I bought that (no point in buying a pack of seeds for one cuke!).
Not really started on the flowers yet, but bought them all in.
My real problem this year (and last) is botrytis on my strawbs. I bought new raised beds last year and all new plants so I am pretty heartbroken. I replanted them all about 6 weeks ago to spread them out more but I don't think it has worked.