My T3 & T4 is high & I am breastfeeding mother - what medicine can I use similar to carbimazole?

Most patients are treated with levothyroxine, or a similar synthetic thyroid hormone. However, natural thyroid hormone supplements from the dried thyroids of animals are still available. Natural thyroid hormones have become less popular, mostly because the concentration of thyroid hormones in the thyroids of animals before they were slaughtered naturally varies somewhat. However, some people are afraid of rare allergic reactions to synthetic pharmaceuticals, and some patients & doctors just prefer natural treatments. Synthetic thyroid hormone contains T4 only and is therefore largely ineffective for patients unable to convert T4 to T3. For these people, natural thyroid treatments hormones are still available. Some natural thyroid hormone brands are F.D.A. approved, but some are not. Thyroid hormones are generally well tolerated. Thyroid hormones are usually not dangerous for pregnant women or nursing mothers, but should be given under a doctor's supervision. In fact, if a woman who is hypothyroid is left untreated, her baby is at a higher risk for birth defects. When pregnant, a woman with a low functioning thyroid will also need to increase her dosage of thyroid hormone. One exception is that thyroid hormones may aggravate heart conditions, especially in older patients; therefore, doctors may start these patients on a lower dose & work up to avoid risk of heart attack.

However, since you are feeding mother, it would be recommended to seek medical advice, take care, be safe & well.

Hyperthyroidism is a condition in which the thyroid gland makes too much thyroid hormone. The condition is often referred to as an "overactive thyroid."
Antithyroid medications prevent the thyroid from producing excess amounts of T4 and T3 hormones. There are two types of antithyroid medications used in the US —propylthiouracil and methimazole.
Both propylthiouracil and methimazole are excreted into human milk. Both the manufacturers consider propylthiouracil and methimazole to be contraindicated during lactation.
However, propylthiouracil is considered compatible with breast-feeding by the American Academy of Pediatrics.
Discuss this with your doctor.
https://www.drugs.com/mtm/propylthiouracil.html
https://www.drugs.com/health-guide/hyperthyroidism.html