Solved!
The ATtiny85 does indeed have room for a bootloader: micronucleus which is used by Digispark to allow USB connection for their ATtiny85 based boards.
However, what I was looking for is to load both code and bootloader with a single hex file.
Now that is superseded by downloading the micronucleus bootloader in a fully erased ATtiny85 with a USBtinyISP or its chinese clone . Then with AVRDUDESS , which is a userfriendly GUI for avrdude, this hex file can be programmed in an ATtiny.
Thus bypassing the need for a combined code+bootloader hex file.