Combining the outputs of multiple SPI devices
Slaves with chipselect inputs are not a bad idea. This way will cost many ports of your MCU, but if you have this resources, I recommend to stay with this idea.
If you are familiar with RTOS (freertos.org is a free good option) you can implement some code like a SPI driver to share and switch the communication through all slaves. I did this in some of my projects. I called my driver "SPIShared".

By using a RTOS mutex you will protect each slave to do a complete transaction with your master. After that, the mutex is released to allow a new communication.

Observation: you can make a shared SPI even though each has a different slave standard. Before each transaction you will need reinitialize your SPI peripherical with the slave communication standard.