Older mom needing tips for trying for baby #3 soon....

Hi all! Im Candice from fl. I have a 13 yr old son and 9 yr old daughter from previous marriage. My bf of 8 years wants us to start trying for a baby as soon as he gets back. Hes military. Wont be here for 12 to 36 months. Im looking for ways to boost our chances myself on my end before he returns. Im 40 and hes 26 atm. We had 3 losses a few years ago and stopped trying for a bit because the emotional damage it was causing us after the last loss. Losses were a chemical. A very early miscarriage (before 6 weeks). And.a loss at 9w 4d (this one hit the hardest). So mamas. Any tips on supplements. Exercises. Foods. Creams. Etc. Id be very grateful. At 40 im so scared this won't happen. I it for me...but for him more. He was devastated. Any tips tricks etc is appreciated! Also items and things i should buy for ttc before he gets home! Ty!