For a low cost solution to help with dryness I have often used gel crystals mixed in with the soil below the surface.

I have also used them in the bottom of individual planting stations and they were effective for years. It isn't a substitute for increasing the humus content but it would tide you over until you have more compost.

If you have a lawn you can spread the mowings over the ground as a thick mulch over the winter, together with any mown chopped leaves you can come across. This may reduce the nitrogen content of the soil temporarily but you can replenish that with fertilizer in the spring and it does help the soil texture for free..

Hope you checked that the new topsoil didn't reach the trunks of the conifers.

Depends what you mean by not too costly really - I'd head to the garden centre and pick up some composted animal manure, around a fiver a bag, they often have a deal on like buy 3 bags get one free.

Thanks to Steragram and Bamboo for suggestions.
I will get some composted animal manure and use the other ideas too.