Optiboot | Optimised bootloader for Arduino

I'm trying to build a small hygrometer based on the DHT11 and I'm having a bit of an "issue" with the code size. I want to run it on an Attiny45 and it's a wee bit too big (352 bytes too big to be exact). I am aware that I could just use an Attiny85 and have space to spare or don't use a bootloader and barely fit it in (94%) but I kind of want to make my life harder than it needs to be and figure out how to reduce size since it'll probably come in handy in the future. Treat it as a learning experience if you will.

What it's supposed to do:

• Read DHT11 input
• Display results on 2 two-digit 7-segment displays (so I guess 4 7-segments in total)
• Go to sleep most of the time to preserve battery
• Wake up every 8 seconds to update sensor values (without turning on the display)
• Wake up on a button press to display the values for humidity and temperature

Side note: 7-segments are adressed via two 74HC595s of which I am using 7 outputs each for the displays and 1 each for a transistor that connects the display in question to GND. There's a schematic at the bottom if you're interested.

As pointed out, my main issue is code size so if anyone has any tips on how to reduce that (or any other tips how to improve the code) please let me know.

I hope I'm asking the question properly, if not please let me know.

Compiler output: