Raise the terrace, but how? Possibly pedestals?

Hello dear experts,

we want to lay porcelain stoneware tiles (Unicom Starker Debris) in 60x120cm on our terrace. The manufacturer offers options with increased slip resistance in both 10mm and 20mm thickness.
The terrace needs to be raised by about 15 cm compared to the current one. In addition, we will extend about 1 m beyond the current base area into the existing lawn area.
So far, the terrace is made of rough sandstone slabs lying on sand/gravel. I do not know the exact construction and depth, but there have been no cracks or other problems in the last 20 years.

We currently have 2 offers.
Provider 1 wants to tear out the old terrace and build a completely new structure with a concrete slab. For a lot of €.
Provider 2 wants to concrete over the old terrace (plus, of course, an extension into the lawn). For still a lot of €.
In both cases, the tiles would be laid in the concrete (or a screed layer).

I would prefer an option with less material movement and lower costs.

Can the thick 20mm tiles not be laid on pedestals?
It is clear that we need a foundation in the current lawn area, but a strip foundation would be sufficient there, right?
What other options do you see?

Panels in 2 cm and the size without adhesive are looked at very, very critically by many. I googled a lot and asked around in advance and most said that they have to be glued. We were also very uncertain and laid panels with 90x45x2 in a gravel bed last year. Very narrow joint with sweeping sand. Underneath is compacted crushed stone and edged concrete curbs all around. So far we are very satisfied except for a few beginner mistakes (2 panels wobble, front edge sticks up too high so that green deposits form there over the winter and cleaning is somewhat difficult). But these would be correctable if we made the effort. Support pedestals at this size... I would already be a bit afraid that the panels would break under unfortunate load?!

Large tile formats are currently popular outside as well.

After research, my personal conclusion was:
Thin tiles (up to 2 cm) laid on gravel will potentially shift or wobble sooner or later; if using tiles, then rather on a solid foundation - with possible risk of frost heave/joint damage.
Pedestals also require a water (drainage) layer underneath.

We therefore ultimately decided on natural stone (local graywacke from Lindlar) (100 x 50 x 4), flamed surface and laid on gravel. The slabs weigh 60 kg and lie solidly and securely (and can be picked up again). Slightly more expensive (but not by much), but easier/cheaper to lay.
Very pleasant underfoot, only minimal algae in spring, which are scrubbed off with some hot water and swept away dry. In summer it doesn't get too hot etc.

Our terrace is also elevated (still visible 20 to 50 cm), forming a U-shape on the south side around the house, but the retaining wall was very complex:
Strip foundation, formwork stones with concrete, facing bricks matching the house at the front, projecting wall capping plate made of the same natural stone (with rain groove) at the top, inside in front of the wall capping plate a "hidden" Aco slot drain which channels ponding water over the terrace slope.

Simpler solution: planting stone as edge support (or formwork stones).

My parents have just had 75x75x2 laid on pedestals. I don't like it. Apart from the fact that it sounds strange when walking, it's also practically impossible for no panel to wobble.