"...but only if they will survive in thinnish soil with little extra irrigation."

Hydrangeas are not going to work. Note the "hydra" in hydrangea. They need average-to-rich, moist soil.

Actually, oakleaf and panicle hydrangeas are more tolerant of drought or dry soils and lots of sun than other species. And while 'hydrangea' loosely translates to 'water vessel' from the Greek, that refers to the shape of the seed capsules, not the plant's desire for water :-))

Irrigation will very likely be required but not to the same extent as other species demand.

IME, arborescens are water hogs. Paniculatas are not bad here in drought. You may or may not like the look of the dwarfs. They supposedly stay small, but are new to my garden.

The only comment I have on oakleafs is that they aren't reliably hardy here.

My oakleaf is getting huge. I never water it. We have had recently about 6 months or at least 5 with very little rain. I have to water my lacecap hydrangeas in those conditions. Soil is not water retentive. I planted a Limelight a couple of years ago under a big oak tree. It gets sun from angles. I've watered it once or twice in that time and it has held up well. The dry flower heads are attractive in winter. I like the lime color but might like it better if it stayed white. Limelight gets big very fast. It is legal to propagate it now and it roots easily.

My D-i-L has hydrangeas (mostly macrophyllas) in pots...and I know she is less than fervent about watering so I assumed they would not be utterly hopeless ONCE ESTABLISHED. I had a limelight and an oakleaf in the wood and while they are not really thriving, they are not stone dead either unlike the magnolias which absolutely cannot survive without extra water (ask me how I know?) My dwarf arborescens was a one season plant, along with a coupla persicarias I had foolish hopes for, so I am going to try another paniculata - maybe Little Lime?

I am going to look at Early Evolution too, Rouge. I am fine with pale pinks...I just don't care for the likes of 'Wims Red' .One I really like is Runaway Bride (despite terrible name)...do you think, with a little effort, this might be a goer for me?.

@rosaprimula UK (Cambridge) Z8/9 I dont think you can consider 'Little Lime" as being....little; once fully grown as it is advertised as up to 5 foot by 5 foot at maturity.

One I really like is Runaway Bride

Not sure if this is the same (but renamed? for a NAmercian audience) but I potted up a Fairytrail Bride this past April and by later in the summer it was not looking so good. I wonder if it is a bit of what @ken_adrian Adrian MI cold Z5 would call a "foofoo" plant...or maybe/probably just me.

https://www.provenwinners.com/plants/hydrangea/fairytrail-bride-cascade-hydrangea-hydrangea-x