As you are self employed you might need to change the way you do taxes so you make more on paper... or you should pursue a W2 job as income is calculated by paystubs not taxes from the previous year.
The financial requirements for I-129F are not as high as the financial requirements for adjustment of status.
But, to be safe I would make sure you meet the requirements for the I864 when you complete the I134.
If you were to submit the affidavit of support right now you would need to be making $31,075 a year or have at least $93,225 in savings. - this amount will increase by the time your partner's K1 petition is approved and she attends her interview.
If you are unable to increase the amount you make on paper- you need to find a joint sponsor to sponsor both your fiance and her child.