1st make sure you are tracking conversions. You can track leads, sales and revenue amount.
Then look at your impression share % for each campaign & ad group. This will let you know what share of impressions you are currently receiving, and you can derive what budget you should have to receive 100% impression share. Since you are not increasing your bids, you should receive similar performance as you increase your budget. ...CPC, CPA,CPL metrics.
Next step is to improve your text ads..the higher your CTR, the more clicks you will receive, which will increase budget ...however this will also increase your quality score, and lower your CPC. Quality Score takes weeks/months to improve, its not an overnight improvement. Focus on increasing Click Thru Rate & Quality Score and you will increase spend, while your campaigns perform better.