I understand about the urgency to train your baby for bottle feeds. I was consumed by it during my maternity because I was returning to work too.
Too many changes will not end with good results. Try tackling one issue at a time. Bottle feeding first. Formula second.
Bottle training:
1. Taste your breast milk. Excess lipase, enzyme that hleps breask down fats for digestion, can make the milk taste soapy. Freeze and thaw milk with excess lipase can make it taste like a rusted can. To test, express your breastmilk. Taste immediately to get familiar with what your breastmilk taste like and taste again 12 and 24 hours later to check for taste change. Also, freeze and thaw to test taste. If you have exces lipase, use a bottle warmer and meat thermometer to heat milk to 148F for 1 minute while swirling constantly and then use an ise boath to cool down. Use right away or freeze.
2. Try different bottles and nipples.
3. Try different feeding positions.
4. Try gently movement. Rocking. Up and down.
5. Try different rooms. Darken room. Limit distractions.
4. Do not wait until she is too hungry and become too fussy to take the bottle.
5. Drip some milk on her lips so she can taste it and gently ease the nipple into her mouth.
Formula: You are a good mom and are making choices that are best for her. I would like to encourage you to continue to breastfeed. I pumped 3 times a day (work and home) and breastfed anytime I could. To be honest, it was hard work. It kicked my butt a few times but I am proud that I met my goal and went beyond it to 1 year. Sounds like she prefers breastmilk. The first 6 weeks of breastfeeding are very hard. Afterwards, it become routine and effortless because babies latch on easily and milk supply is established.
Your daughter sounds like a healthy baby. Keep track of wet and dirty diapers. She is gaining weight and thriving, then no worries about her size.
Good luck and keep us posted.