what to do with a small, sloping, clay back garden...?

[vmcd28]

I have 2 DSs, age nearly 1 and nearly 7.
We have a small back garden, 7 or 8m by 7 or 8m, at a guess, which slopes downwards from the house. The soil is basically clay, so it's constantly like a swamp at the bottom.
The bottom of the garden almost levels off for a few feet, where we have a slide and a small trampoline.
SO, what I'm wondering is what to do with it, so it is useable space, rather than only useable during very dry spells.

Also, living next to some woodland, we are always struggling with hellish weeds through the lawn, inc thistles and creeping buttercup. Theyre taking over, and lawn weedkillers just havent worked with them.

I'd half thought of the following options -

1. Put some decking at the bottom, to level off some of the slope, where the trampoline can go for now, but it can also be used for a seating area.
2. Pay someone to dig up the lot, and start again. But this will likely be extortionate.
3. Terrace it onto two levels. Again, I'd imagine this would be very expensive.
4. Dig up the lot and top it all with very-realistic artificial lawn.
5. Get drainage put in, BUT one of our neighbours has done this, and says it hasnt worked well.

Can someone suggest something, or give me a clue as to what sort of price landscapers would charge for this?

What's the height difference between the highest and lowest points? What currently separates you from your next door neighbours? Does the garden only slope in one direction?

I'm nearly at the end of a complete redo of my garden, which was sloping in two directions. We opted to build the slope up and pave that part, rather than terrace it down, but that was largely governed by the access to the alley behind the house, and also the relative levels of our next door neighbours' gardens. Digging down/terracing can involve building retaining walls.

Our garden is a bit bigger than yours, and we're having additional work done, so it's hard to compare pricing, but I reckon paving and terracing could be about £1700.