For those in the US, there are no natural alternative products to treat/prevent benign prostate hyperplasia/hypertrophy (BPH). The only meds used for BPH either shrink the prostate (5-alpha reductase inhibitors or 5ARIs) or relax the prostate capsule (alpha blockers, which are further broken down into those that lower blood pressure & those that don't).
Surgically speaking, transurethral resection of the prostate (TURP) enlarges the urethral pathway thru the prostate (the growth of the prostate compresses on the intraprostatic urethra making it difficult to empty the bladder). The traditional method is to chip away at the prostate, little by little. Newer techniques use laser, heat, cold, radiofrequency, etc to enlarge the urethral pathway.
Because dihydrotestosterone (DHT) appears to lead to BPH, we use 5ARIs to shrink the prostate but this takes at least 6 months. At the same time that one shrinks the prostate, expect your PSA to drop by 50%. If it doesn't, then you have to worry about an underlying prostate cancer. However, by inhibiting the conversion of testosterone (T) into DHT, one can cause T to be converted into Estradiol (E) which can then lead to male breast development (gynecomastia) and/or loss of sex drive (libido) from too much E. This is the most common side effect of 5ARIs but can be controlled to some extent by lowering your E (with an aromatase inhibitor - but obviously this leads to a pharmacologic falling domino effect). I've written about this on my blog in response to a recent study looking at this.
Sympathomimetics, such as over-the-counter (OTC) decongestants, can cause the prostate capsule to squeeze down upon the prostate, again making it difficult to urinate. So try to avoid (OTC) cold & allergy meds best you can. Some OTC allergy meds also aggravate the matter by decreasing the ability of one's bladder to contract and force urine past the prostate. Prescription allergy meds w/o decongestants tend to be ok. But check w/your family physician to be sure.
Prescription alpha blockers do the exact opposite of the decongestants. In other words, they relax the prostate capsule. Their effects occur in a much shorter period of time, measured in weeks rather than months (for 5ARIs).
If you need to lower your blood pressure (b/c you have hypertension), then some of the older meds, such as doxazosin & terazosin are useful (but you have to be careful since they're not the best options and can lower your blood pressure dramatically when changing your position suddenly, eg from laying down to standing up quickly)).
If your blood pressure is fine, then the newer generation, of which Flomax (tamulosin) is one, relax the prostate w/o lowering blood pressure significantly.
With all alpha blockers, you should check w/your ophthalmologist prior to starting to be sure you won't need cataract surgery any time soon since they (alpha blockers) have been associated w/floppy iris syndrome.
Whew. But that doesn't address your request for alternative products. Saw palmetto has been used widely but whether it's truly effective (from a scientific research perspective) is debatable amongst traditional physicians. One of the major issues is the lack of third party oversight for dietary supplements. In other words, you can never be sure that what you're buying is what's on the label. Furthermore, while beta sitosterol is a component of saw palmetto, we're still not sure how/why it (saw palmetto) works or not. Same goes for beta sitosterol.
I agree that with you that I wouldn't necessarily want more estrogen in my body than necessary for the reasons mentioned above. Having said that, I have no experience w/Trinovin or any other OTC supplement that is advertised to help w/prostate issues. Besides the philosophy of avoiding medications when possible, if you want to stop because you're suffering from side effects, chat w/your family physician (or whoever prescribed your Proscar & Flomax) and ask about alternatives. Perhaps you'll do better on Avodart and either Rapaflo or Uroxatrol.
PS DIM (or DIIM) doesn't so much "overcome" estrogens as much as it appears to alter the metabolism of estrogen, shifting its breakdown products from cancer-prone to more benign forms. It is found in cruciferous vegetables, eg broccoli, cabbage & cauliflower, consumption of which has been associated w/lower cancer risk.