Bulbs - most bulbs that are easy are planted in the autumn not spring so you've missed the window for it. I do recommend doing that in time as although it's time consuming to do, it gives you years of easy, colourful gardening in springtime when nothing much else is in bloom.
Seeds - are cheaper in theory, but require a lot more effort. Look for deals on seeds in shops or online. Try not to spend more than £1 on a packet unless it's something you really like. You can show direct from early May but you will get better results (and less slug damage!) germinating seeds in seed trays indoors from now - but that requires a bit of space and more money (at which point it can work out cheaper to buy plants). However annual seeds such as poppies, cornflower, nigella, cosmos are particularly easy to grow outdoors only, will self seed for the next year and go easily so are worth getting. (Try to get more dwarf small varieties of seeds if you can as it seems to work better)
Plants - this can get expensive quickly. Understanding what you are buying is a must. Perennials will last you more than one year so are generally much better value for money than annuals (unless you buy something self seeding). But take a note of how big they get. You will need less than you think. Grasses are ornamental and can give you easy to maintain interest all year round. Same with shrubs - but again look at how big they get.
For me a mix of bulbs, some annual seeds, perennial plants, a few grasses and a few shrubs are the way to go. You can get a really nice result from limiting how many species you go for (already mixing it up is better for biodiversity).
Start by picking your shrubs, then grasses, the perennials, then fill in with annual seeds in the gaps and plant bulbs in the autumn - amongst your perennials and annuals - so they come up first.
But yes - direction and soil type are important to note before you do any of this - many plants don't do well if they are in shade most of the day.