Infill for raised beds

Hi folks - newbie here looking to pick your brains  So please be patient....

I'm well on with a total redesign of our very compact rear garden. It features a circular central patio, and raised beds to rear & either side to surround this. The beds vary in height - 450mm/600mm. Rather than buying tonnes of topsoil, is there any kind of lightweight infil to bulk up the beds - say for half the depth - then going with topsoil on top? Or am I best going for soil, soil & more soil, if this is best for the roots??

Apologies if this message appears twice - the computer just burped!

The best way is with soil, and add well-rotted compost and manure as you go. Make sure you inspect the supply source before you buy it, checking for weed and twitch infestation. Take two or three bucketfuls from various parts of the supplier's stock as samples; if it's in heaps, dig into the middle of the heap. When it's delivered, don't accept anything that doesn't match your samples - and no clay, builder's rubble, litter and so on. If they're not willing to show you where the soil came from and guarantee against perennial weeds then look elsewhere.

Excellent - thanks Joe_the_Gardener

It's worth giving your local council a try, many sell bags of soil conditioner/ compost made from recyled waste and it's cheaper than the garden centre. some may sell in bulk, it worth enquiring.

It depends on what you are growing. If the plants do not need 60cm of soil then filling with rubble will add drainage and lessens the amount of soil required overall.

The trouble is that you might change your mind about what you want to grow - for instance decide to grow a crop of new potatoes or parsnips. I've assumed that bigMAL's site is essentially reasonably drained, so I'd go for all soil and maximum flexibility.

And also, if plants are to be there long-term, they will have more room for root expansion and growth.