For the tax return, probably nothing. There is a good chance that you have nothing to report as income. If you did not gain at least 250,000 on the sale of the house (500,000 if you are married filing a joint return), the gain on your sale may be excluded from your income (being retired does not change this). If unsure, you may follow the instructions in this FAQ: https://ttlc.intuit.com/replies/3300213
As far as the purchase of the new home is concerned, you may deduct the mortgage interest and real estate taxes you paid in the year. Most other expenses are included in the basis of the home, which would be used when the home is sold in the future to determine how much gain or loss is obtained on the sale.